OK then let's see....
If you are 100% confident in your sexual ways, you should be able to do this no problem.
You should be able to, just for the hell of it, to prove a point, be able to let another guy lick and suck on your genitals, or have anal intercourse with you. If you're honestly 100% sure you'e not gay, then you wouldn't get an erection at all.
Now you may say that just doing these acts would make you gay period, wether or not you'd get turned on by them, but we know that's really not the case. Simply performing an act means you are acting it out, and may or may not feel the way you are acting. If you actually got aroused by it, then that's a different story, that would definately mean you're gay.
So who here in their heart of hearts can muster up the courage and is confident enough that they can actually do something like this without getting turned on?