A couple of things I say more often would be "Don't kill me, it hurts!" and whenever my brother messes up a sentence I used to say "Go get the words!" Which I guess is an inside joke because it originated from a jumbled conversation we had, but still kind of funny.
Oh yes, in a couple of infection games with one group, all the zombie players would start saying "Brainnnnsss..." in zombie-ish voices when they got within audio range of the survivors, so I decided to start saying other organs, my favorite is still "Luuuuuuuuuunnnnnnnngssssss..." I now do this everytime the other zombie players say "brains," which isn't often so it doesn't get old for me... sorta.
Lastly, while playing the last level of campaign in Halo 3, with all four of us in ghosts, two of the others and I started singing the ending level song, with two of us doing the gregorian choir part and one doing the orchestra parts with "da da da daaaaaa, da da da daaaaa" and so on, it was fun, but we had to stop, because the 4th guy was from the UK and it was 2 AM there, he didn't think it was funny, and if he left we would have had to start all over again for the achievement, we finished and I had just enough time to say "Thanks for putting up with us and staying" before he quit.