Some of the unlockable titles are nods to other games, media, and events. What better way to make an online friend than to demonstrate that you both get it while the others are just clueless? Here's some of the more notable of the Call of Duty: Modern Warfare 2 call signs' titles.
Shock and Awe - One of the more memorable of missions from Call of Duty 1, but also the name for a devastating military tactic.
BOOM! Headshot! - Reference to a popular viral gaming video; Undoubtedly quoted by players in-game endless several times a match.
All Your Base - Reference to a famous mistranslation (the full line being "All your base are belong to us") from the game Zero Wing.
True Liar - A play on the Arnold Schwarzenegger film "True Lies".
Get to the Choppa! - Another Schwarzeneggar-related title, this time being a quote from the film Predator.
Behind Enemy Lines - Thinly veiled reference to the Behind Enemy Lines film.
Big Brother - Obvious reference to the ever-watching Big Brother.
My Li'l Pwny - Obvious reference to the early "My Little Pony" series and franchise.
Broken Arrow - Reference to the John Travolta film.
Click Click Boom - Reference to the song of the same name.
End of the Line - Master Control Program quote of Tron fame.
Companion Crate - Thinly veiled reference to the companion cube from Portal.
Live Long - Reference to the "Live long and prosper" quote of Star Trek.
Five Sided Fistagon - Reference to the "Bulls on Parade" song of Rage against the Machine.
Great White North - Reference to the Great White North TV show.
Rolling Thunder - A reference to the "Rolling Thunder" bombing campaign that took place during the Vietnam war.
Fire and Forget - A phrase normally associated with the firing of Javelin missile launchers.
Droppin' Crates - Reference to the Disturbed song: Droppin' Plates.