Allen is going to be a mess. He's the king of lying, so saying the first thing that comes into his head might sometimes be the truth and might sometimes be lies just because they're that ingrained, and he might fluff all over people he has crushes on, and god help you if he has mixed feelings about you.
Do you have long, pretty hair? If so, Flynn is going to pet it! Or braid it! Come line up! :D
Neku I don't even know, man. He might lose his inner monologue? I haven't even introed him yet, give me a break.
Roxas is... going to do exactly what he always does, because he's pretty damn honest already.