These are all the Titles that I have unlocked in Call of Duty: Modern Warfare 2 in Multiplayer. I have personally confirmed how to get all 192 of these titles in MW2. This list is alphabetical by title with the challenge that is needed to unlock it.

Some Notes:
99% of these unlock by just going through all the challenges. There are however a few hidden Titles. 4 are gotten for using the Deathstreaks. Toxic is given for getting Nuked in a match, Sidekick is given for getting 5 kills with your secondary and equipment weapons, and Kleptomaniac is given when you get a kill with 2 different picked up weapons.
PERKS – You get a Title at I, the Pro version at IV, a Title at V, and a Title at the final VI.
PRIMARY WEAPONS – You get the Title for finishing Mastery, which is just getting all the attachments.

<3 – Misery Loves Company (Humiliation)
1bullet2kills – Collateral Damage (Precision)
1st Lt. (Levels)
1st Sgt. (Levels)
2fast – Slight of Hand Pro I (Perks)
Absentee Killer – Absentee Killer (Finishing Moves)
Accident Prone – Base Jump (Basic Training)
ACR – ACR Mastery (Primary Weapons)
Airborne – 21 Ton Giant I (Killstreak)
All Pro – All Pro (Precision)
Ambush – Clay-More II (Precision)
Backfire – Return To Sender (Humiliation)
Backsmasher – Back-Smasher (Primary Weapons)
Backstabber – Backstabber (Humiliation)
BAM! – Master Chef II (Elite)
Bandolier – Scavenger Pro V (Perks)
Barrett .50cal – Barrett Mastery (Primary Weapons)
Big Bada Boom – Multi-RPG I (Precision)
Bite The Bullet – Stopping Power Pro VI (Perks)
Blindfire – Blindfire (Humiliation)
Bling Bling – Bling Bling V (Perks)
Blood Brothers – Team Player II (Operations)
Blood Money – Color of Money I (Payback)
Blunt Trauma – Shield Veteran I (Primary Weapons)
Boilermaker – Car Bomber I (Humiliation)
Bombshell – Bomb Down (Operations)
Boom Boom – Multi-C4 I (Precision)
BOOM! Headshot – LMG Expert II (Precision)
Booyah! – Multi-Frag I (Precision)
Bow Down – Crouch Shot II (Basic Training)
Broken Arrow – Airstrike Veteran II (Killstreak)
Bulletproof – Bulletproof (Primary Weapons)
Bullseye – Plastered I (Equipment)
C4 and After – C4 Shot II (Equipment)
Catch Shrapnel – Claymore Shot I (Equipment)
Charity Case – Air Drop Inbound I (Killstreak)
Chick Magnet – Blackout I (Killstreak)
Clay Pigeon – Counter-C4 I (Elite)
Cloak and Dagger – Carnie I (Equipment)
Close Support – Hardline VI (Perks)
Cobra Strike – Helicopter Inbound I (Killstreak)
Companion Crate – Air-Mail II (Killstreak)
Completely Numb – The Numb [Painkiller, Take damage that would normally kill you] (Hidden)
Concussive Barrage – Think Fast Stun (Humiliation)
Counterintelligence – Scrambler Pro VI (Perks)
Crackin’ Skulls – Assault Expert II (Precision)
Darkbringer – Darkbringer (Equipment)
Dead Man’s Switch – Last Stand Pro V (Perks)
Deadline – Hardline Pro V (Perks)
Death From Above – Death From Above (Finishing Moves)
Destroyer – Search And Destroy Victor I (Operations)
Dictator – Dictator (Precision)
Dish the Rock – Point Guard I (Basic Training)
Dishes are Done – Break The Bank (Payback)
Disruptor – Scrambler Pro I (Perks)
Double Down – Bling Pro I (Perks)
Drifter – Vandalism (Basic Training)
Dronekiller – Dronekiller (Finishing Moves)
Droppin’ Crates – Droppin’ Crates (Finishing Moves)
DZ Clear – Air-Mail I (Killstreak)
Early Detection – Bomb Prevention I (Operations)
End of Line – End Game II (Killstreak)
Enemy With Benefits – Group Hug (Precision)
Excalibur – Comando VI (Perks)
Explosive Ordinance – Search And Destroy Victor II (Operations)
Faceoff – Assault Expert I (Precision)
Finishing Touch – Finishing Touch (Finishing Moves)
Fire and Forget – Sentry Veteran II (Killstreak)
Flatliner – The Brink (Elite)
Flying Tank – 21 Ton Giant II (Killstreak)
Flyswatter – Flyswatter (Basic Training)
FNG (Levels)
Frag Out! – Grenade Kill I (Equipment)
Friends With Benefits – The Resourceful (Elite)
Full Arsenal – One Many Army Pro I (Perks)
Full Force – Danger Close I (Perks)
Full Throttle – Helicopter Inbound (Killstreak)
Gen.
Get Real – Hardcore Team Player I (Operations)
Get to the Choppa! – Chopper Gunner Veteran I (Killstreak)
Ghille in the Mist – Ghille in the Mist II (Basic Training)
Ghostrider – Air To Ground II (Killstreak)
Givin’ Static – Interference I (Killstreak)
Global Thermonuclear War – End Game I (Killstreak)
Godhand – AC130 Veteran I (Killstreak)
Grassy Knoll – Ghille in the Mist I (Basic Training)
Hands Free – Sentry Veteran I (Killstreak)
Hard Target – Airbourne (Precision)
Hard To Kill – Last Stand Pro I (Perks)
Hardcore Only – Hardcore Team Player II (Operations)
Headrush – SMG Expert I (Precision)
Heartbreaker – Scrambler Pro V (Perks)
Hi Def – Hi Def (Finishing Moves)
High-Caliber – Stopping Power Pro I (Perks)
Highlander – Flawless (Precision)
Hot Shot – Defuser I (Operations)
How The ? – How The ? (Elite)
I.C.E. Man – Counter-C4 I (Elite)
ID Thief – Identity Theft (Payback)
I’m Rich – I’m Rich I (Payback)
Impaler – Comando I (Perks)
Intergalactic – Sabotage Victor II (Operations)
Invisible – Cold-Blooded Pro I (Perks)
Iron Lungs – Steady Aim V (Perks)
It’s Personal! – It’s Personal! (Equipment)
It’s Sabotage! – Sabotage Victor I (Operations)
Jack In The Box – Jack-in-the-Box I (Equipment)
Joint Ops – Point Guard II (Basic Training)
Juggernaut – Solid Steel II (Equipment)
Jump Jet – Vertical Takeoff I (Killstreak)
K Factor – Stopping Power Pro V (Perks)
Kill for Good – Multi-RPG II (Precision)
Kleptomaniac – Renaissance Man [Get a kill from 2 different picked up weapons] (Hidden)
Last Resort – Last Resort (Finishing Moves)
Lights Out! – Think Fast Flash (Humiliation)
Live Long… – Survivalist (Elite)
Living Dead – Living Dead [Final Stand, Get up after getting put into Final Stand] (Hidden)
Lone Wolf – Free For All Victor I (Operations)
Low Profile – Prone Shot II (Basic Training)
M4A1 – M4A1 Mastery (Primary Weapons)
Mach 5 – Mach 5 (Precision)
Mad Men – Bang For Your Buck I (Payback)
Maj. (Levels)
Martyr – Afterlife [Martyrdom, Kill someone with your Deathstreak (Hidden)
Mastermind - Claymore Shot II (Equipment)
Mmmmm Brains - Both Barrels (Elite)
MOAB - Ultimate Sacrifice (Intimidation)
Money Shot! - Money Shot (Payback)
NBK - NBK (Precision)
Nerves of Steel - Steady Aim VI (Perks)
New Jack - ATM (Payback)
Ninja - Comando V (Perks)
No. - Marytr'doh [Kill someone who is cooking a grenade] (Hidden)
Noob Tuber – Ouch (Humiliation)
Not in the face! – LMG Expert I (Precision)
OG – OG (Finishing Moves)
OMFG – Cruelty (Humiliation)
Omnipotent – Radar Inbound I (Killstreak)
Overwatch – Exposed I (Killstreak)
owned. – Owned (Finishing Moves)
Parting Gift – Clay-More I (Precision)
Perfectionist – Perfectionist (Precision)
Philanthropist – Special Delivery II (Killstreak)
Pin Puller – Multi-Frag II (Precision)
Pineapple Express – Grenade Kill II (Equipment)
Plane Whisperer – Airstrike Inbound II (Killstreak)
Plastique – C4 Shot I (Equipment)
Pop Off – SMG Expert II (Precision)
Preemptive Strike – Hardline Pro I (Perks)
Pro Gambler – Airdrop Inbound II (Killstreak)
Protect and Serve – Sponge I (Primary Weapons)
Public Enemy – MVP Team Deathmatch (Operations)
Pushin’ Daisies – Goodbye (Basic Training)
Pyromaniac – Backdraft I (Basic Training)
Quickdraw – Fast Swap (Elite)
Rainmaker – Overdraft (Payback)
Re Zero – Ghille in the Mist III (Basic Training)
Reign Down – Attack Helicopter Veteran I (Killstreak)
Rejected – Backdraft II (Basic Training)
Reloaded – Scavenger Pro I (Perks)
Remote Viewer – X-Ray Vision I (Basic Training)
Reversal of Fortune – Counter-Claymore II (Elite)
Rival – Rival (Humiliation)
Robin Hood – Robin Hood I (Payback)
S.S.D.D. (Levels)
SBD – Stealth Bomber Veteran II (Killstreak)
Sgt. (Levels)
Share Package – Special Delivery I (Killstreak)
Shot Down – Crouch Shot I (Basic Training)
Sidekick – Sidekick – [5 kills with Secondary/Attachments/Equipment in a life] (Hidden)
SIGINT – Interference II (Killstreak)
Silence – Did you see that? (Equipment)
Silent Strike – Ninja I (Perks)
Skeet Shooting – Hard Landing (Humiliation)
Smash Hit – Smasher (Primary Weapons)
So Baked – Master Chef I (Elite)
Solid Steel – Solid Steel I (Equipment)
Sonic Boom – Danger Close V (Perks)
Speed Demon – Lightweight I (Perks)
Squawk Box – Attack Helicopter Veteran II (Killstreak)
Starfish Prime – Blackout II (Finishing Moves)
Stickman – Stickman (Finishing Moves)
Streaker – Fearless (Precision)
Stuck on You – Plastered II (Equipment)
Stun Gun – Slow But Sure (Humiliation)
Submit To Authority – X-Ray Vision II (Basic Training)
Sureshot – Steady Aim I (Perks)
Surgical – The Surgical (Precision)
Survivor – The Survivor (Elite)
TacDel – Tactical Deletion (Equipment)
Ta-Da! – Jack-in-the-Box II (Equipment)
Tag! You’re it! – Hot Potato I (Humiliation)
Take A Stab – Carnie II (Equipment)
Tango Down – Prone Shot I (Basic Training)
Team Player – Team Player I (Operations)
Techno Killer – Techno Killer (Finishing Moves)
The Anarchist – Multi-C4 II (Precision)
The Bomb – Bomb Defender I (Operations)
The Denier – The Denier (Intimidation)
The Domino Effect – Dominoes (Elite)
The Feared – Free For All Victor II (Operations)
The Invincible – Invincible (Elite)
The Legend – Last Man Standing (Operations)
The Mad Bomber – Saboteur I (Operations)
The Mastodon – Star Player (Elite)
The Specialist (Levels)
The Watchman – Radar Inbound II (Killstreak)
Think Fast! – Think Fast (Humiliation)
Time is Money – Time Is Money I (Payback)
Time on Target – Airstrike Veteran I (Killstreak)
To The Extreme – MVP Team Hardcore (Operations)
Toxic – Radiation Sickness [Get Nuked] (Hidden)
Trackstar – Marathon Pro I (Perks)
Transformer – Transformer (Finishing Moves)
True Liar – True Liar (Finishing Moves)
Unbelievable – Unbelievable (Finishing Moves)
Unbreakable – Unbreakable I (Primary Weapons)
Voyeur – Exposed II (Killstreak)
Wargasm – Wargasm (Intimidation)
X-Ray Vision – SitRep Pro I (Perks)