TOMA! TOOOMA!
Taken from my brother. In spanish, "tomar" means "to drink" but it also means "to take" so TOMA! (toh-mah) translates into a sort of "TAKE THAT!"
It's not so much the word, it's the loud and mocking way you say it.

"THANK YOU GOOD SIR FOR ALLOWING ME TO KILL YOU"

"I am Death.....come with me"

BITCHES?

"PECKER!"

I don't really have one, but if I had to pick one, I'd probably end up using "GO FOR THE EYES, BOO. GO FOR THE EYES!"
Because Minsc and Boo are AWESOME.

SPOON!
Ok, I clearly stole that one. I don't really have one. I'm kinda the quiet type.

Stolen or not, it's awesome! God love The Tick!

The only combat I've done lately is against the copperheads in my yard. If I recall correctly, the sound I made while swinging my two-handed shovel over my head and onto their heads was something like, "HRRUGH!" I should come up with something better, though I'll need to be sure not to frighten the neighbors.

Yes, that would be "You, my dear sir/madam are from now on my property! Please clean my genitalia, it itches."

SUCK IT DOWN!

I usually go for a hearty "For Crom!". I've kind of gotten used to not saying anything, as I usually sneak around in games which will allow it; so somehow shouting makes me feel like my location will be given away ¬.¬

"FOR THE PONY!"