Homosexuality describes sexuality, not sexual activity. He'd only be gay if he was attracted to the penis in question, though transgender folk do raise a grey area. In short - he can fuck men and still be 100% heterosexual.
That's gross I wouldn't be proud of sucking a tranny cock or any cock. IMO, if you're a guy and you enjoy penis... you're gay... whether it be a tranny, a man, or a dog..... or cow..... or alien. anything with a penis.
Genetics and human sexuality are very complex things. Both act on a scale of subtleties, it isn't such a black and white issue. There are people that have both functioning organs, known as mosaic hermaphrodites. Seeing a tranny and thinking they are attractive does not make you gay, neither does your childish unnecessary labeling. Anyone who actually wants to be educated on the subject instead of spouting their ignorant bullshit should research what is called "The Kinsey Scale of Sexuality."
I would totally let a chick with a penis do me, Some trannys are pretty damn hot and make jealous lol.