Watching Pitch Perfect again, and through the riff-off, and it seems like the Trebles broke the rule of "stealing the song by picking off a word that they are singing and making it your first word." In the "Songs about Sex" section, the Bella's are singing "Cause I may be bad, but I'm perfectly good at it", to which a Treble broke in with "Sex, baby. Let's talk about you and me." Is it Treble favoritism, or am I missing something?
The lyrics for song being sung by the Bellas:
'Cause I may be bad, but I'm perfectly good at it
Sex in the air, I don't care, I love the smell of it
... and by the Trebles:
Sex, baby. Let's talk about you and me.
So it looks kosher to me as the guy riffed off the next word, sex, which was just about to be sung.