This a weird variation of "asking for a friend". You'd think the "friend" would be the tranny fucking faggot, but this is a likely Spez alt on a tranny sub, so that's far from the weirdest thing in this post. I'm going to go out on a limb and say that the "friend" doesn't exist and this faggot is just refusing to come to terms with his homosexuality. Anyway, quote time:

If it's gay for a man to be with a trans woman, that means it's straight to be with a trans man. Ask him if he'd be comfortable fucking a dude with a vagina, he'll change his mind real quick.

Imagine being such a coomer that the only reason you would turn someone down for sex is if they don't match your sexual orientation. Fucking a FtM troon isn't gay but it is disgusting if she's chemically or physically mutilated herself, and it's sticking your dick in crazy in any case.

Ask him if sucking/taking a strap-on on a cis woman is gay.

This a borderline case. If you want to be overly technical about it then no it's not gay since there's no man on man activity going on. In practice if a dude is into getting his mouth and ass fucked by a dick shaped object then I'm questioning his sexuality. As I've said before, if you have to ask if something is gay the answer is probably yes.

If he says yes, his definition of gay is just in part "bottom" and he's unreachable.

Does this degenerate not realize that there's a difference letting a (real) woman ride you and imitating faggots?