There was another discussion related to dialogue ideas, but here's my interpretation.

Demoman
"AAGH! (laughing) This ain't bloody real.
(Screams and then laughs.)

Engineer
"Whoa! What in tarnation?"

Scout
"AAH!! WHAT THE FREAKIN'-!"
"THIS CAN'T BE REAL! THIS CAN'T BE REAL!"

Medic
"(After bread monster bursts out of Medic's chest) Hmm. (Gets bitten) Das tut weh!" (Translation: That hurts!)

Soldier
"What in the name of-? Come back here! (Bread Monster goes back inside Soldier's chest.) Huh? (Sighs.) Never mind."
"Holy art of war! You won't get away from me! (Looks around.) Damn."

Spy
"Mon dieu! (Monster gets back inside Spy's chest.) As long as there's no blood on my expensive suit.

As for the Sniper, I don't really have any ideas. For the Pyro, maybe reuse some of the existing sound files for him.

Let me know what you think of my ideas!

P.S. Great taunt, CobaltGemini!