Hey I am definately NOT gay and I think its kind of hot when a chick farts so that isn't a good litmus test. That probably just makes me a freak!
I also love anal, with women that is. Again, bad litmus.
I think the threesome thing would work best, just ask him if he has ever been with two other people, take it from there. I would guess if he is half a fag he would be into a threesome with a guy and a girl. Sorry but yuck! I have had some threesome's but always without another cock present thank you very much. Whatever floats your boat.
I have noticed that tons of guys nowadays seem gay. Men have been demasculated by our wussy society. Its hard to tell who is gay anymore.