I haven't had a "full" sexual encounter with a guy, beyond a fellow kid trying the "you show me yours if I show you mine" gambit when I was really young. For whatever reason I didn't like the idea and (pardon the pun) blew him off. I also had a gay friend talk me into dropping my pants once. After a touch or two, that was enough for me.
I have, thanks to Ms. Nathalie Lefebvre, had an opportunity to explore some play with strap-ons recently, and here's what I've learned from that:
-- sexual desire is a lot more complicated than just "I like girls", "I like guys."
-- The first time I put a dildo in my mouth, it was ... weird. I had to ask whether the arousal I felt at doing that meant that I had gay tendencies or not.
-- I feel at this point I am a pretty firmly straight dude with some desire to play with gender roles.
Would I suck a dick, attached either to a guy or a t-girl? I'm really not sure at this point. Given the circumstances? Perhaps. But it's not something that I've fantasized about or in search of. Would it make me gay if I did? Nope. Just a guy who likes girls and sucked a dick once. Does it matter? Not a whole lot, IMO.
I think splitting hairs over dictionary definitions of straight, gay, bi, asexual, whatever, just distracts from the realities of how sex exhibits itself in people's lives.