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.
After listening to the soundtrack for this movie, I firmly believe now that this may have been a directorial mistake. In the soundtrack, the Treble's steal the song at the appropriate time. However, as stated, in the movie, it's about 4 or 5 words too late.