Fauchard1520
Adventurer
My pet peeve is pictured right here. How about the rest of you guys?
Mine is undoubtedly when players can't find a reason for their characters to trust and get along with other characters and/or can't imagine why the character would want to pursue the adventure hook or participate in particular scenes.
It's an offshoot of the "It's what my character would do..." issue. Well, sweetheart, maybe you should start making characters that do get along and trust fellow PCs and do participate.
I combat this issue by helping the players establish ties between their characters and the adventure scenario so as to create the necessary context for said players to participate in good faith.