well, Mark Nut. i've actually caught myself saying it out loud when i make good shot/throw. also, not exactly favourite, but definetly memorable (but rather dark) gag is achievement hunter talk-about-celebrity-they-die gag
The Ryan/Meg joke are pretty funny, in one recent let's play they missed out on a chance to make a really good one though, when Ryan was asked "who's ass he has been eating?" He should have said "Ask Meg"