Taken from another post I made on someone else's discussion:

Scout:
"You're so handsome... but so dead!"
"Can't outrun the best!"
"Let a REAL Scout run this!"

Soldier:
"Lift the helmet when fighting me!"
"Rockets ain't gonna do crap!"
"Drop and give me 20! If you can!"

Pyro:
"That flame retardant suit don't stop BULLETS, do they?!"
"Just try and talk back!"
"Quiet down, mumbles!"

Demoman:
"Try sobering up next time!"
"Can't hit what your good eye can't see!"
"Just TRY and swing that at me!"

Heavy:
"You look like you ate a country!"
"Try hitting me next time, gravy veins!"
"Ya got BIG, MEATY, FISTS!"

Engineer:
"Build me a schematic on THAT, hardass!"
"The hardhat ain't gonna do crap, smartass!"
"Brains won't save you now, dumbass!"

Medic:
"Medicine won't do crap now, nurse!"
"Try resussitating THAT!"
"Maybe your boyfriend will give you mouth-to-mouth!"

Sniper:
"Try AIMING next time!"
"Can't hit what ain't in your sight!"
"Hard to shoot someone when you're DEAD!"

Spy:
"Dead ringer? What a joke!"
"Try backstabbing me NOW!"
"I got blood on your suit! Wadda you gonna do about it?"

All Class:
"See ya in 5 minutes, asshat!"
"Gonna keep killin' you until you ragequit!"
"Death is only the beginning your humiliation!"