why did people laugh when ryan asked aaron kelly if he liked justin bieber on american idol?

Probably because it would be weird for a 16 year-old boy to like a guy who's music is mostly for pre-teen girls.

Ryan Seacrest is regularly asking questions that go far out of the range of what is of interest to the regular music listeners -- he was even uncomfortable last Thursday with speaking with Alison Iraheta who he had known much of last season. Don't mock Aaron for the highly paid "host" who stumbles around with little that is pertinent as far as the show. Keep in mind that he often quarrels with another egotistical "Center of the Idol Universe" (i.e. Simon Cowell).

Because most guys don't like Justin Bieber but I'm assuming Aaron is gay so he just might like Justing after all.

I wasn't sure if Aaron knew who Justin Bieber is! They either laughed at that, or that it was a stupid question. ;)

Because he SHOULDN'T like Justin Beiber. Only 10-year-old girls and Justin's mom should like him.