Iv been watching some gameplay vids and Iv noticed on numerous occasions that after getting a kill, your character makes a cocky comment. Some of the ones i have seen are: " Who wants some?" "Get some" "time to kick ass" and my personal favourite, "Aint that a [censored]"
I personally think this is totally freakin awesome! (Freak out moment over and done with)

I hope there are plenty more phrases in the full game!