I don't think it's fair to say that everyone is a bit bi just like it's not fair to say that everyone is a little bit straight.
I just wrote a book (
Toby) on a male bisexual prostitute living in Barcelona (it's not out until June) and I was fascinated by this guy's story. He's truly 50% bisexual. Like the guy really enjoys sucking cock and eating pussy banging any hole and finds both women and men equally hot regardless of gender. I thought that was fascinating as I always thought most bi guys would lean either more towards straight or more towards gay.
But going back to the original question on this forum, some of Toby's customers were straight men who wanted something quick from him (like a blowjob) and usually when they were high. So I think drugs has a big impact on whether or not a straight guy would suck cock.