I've seen people say they would never want to romance a bisexual character, so maybe that's what was meant?
...I also find that super gross and personally hurtful, so I'm not defending it. 
Well, everyone's got personal preferences. I'm not picky with sexual preferences myself, but I don't see anything wrong with people not wanting to romance bisexual, homosexual, or heterosexual characters. Everybody's got their own tastes, and AJ didn't like the fact that there weren't any heterosexual characters for males to romance, which I can totally understand.
Not being interested in someone doesn't make you a homophobe/biphobe/heterophobe nor hurtful and rude. It's not like he said "I hate bisexual people!", he was just saying "Why aren't there any straight women to romance?", which is valid. You aren't required to have sexual interest in bisexuals or homosexuals to not be labelled biphobic or homophobic. 
Above all that really he shouldn't have to apologize for any jokes or comments he makes. Hypothetically, even if he insulted bisexuals and homosexuals, that's his own business, his own humor, his own content. It doesn't mean you to have to support him and it doesn't mean he's right, but it doesn't give you the position to tell him to do otherwise. Just ignore him and move on. Comedy isn't something that should be apologized for.