Most never cross the line into the actual act but it's fun to prepare them with making them suck a strap on, etc
Yea... until they end up puking in a trash can after You rough fuck thier throat with it

I actually have a long time client who loves talking about doing exactly that--- we discuss how his gay Master would train and enslave him. In sessions I train him to be a better slave for his dream man he eventually meets and becomes property of. He also sees male escorts (on his own accord) and films it so I can give him a review of how well he sucks cock.
Definitely not my bag but I absolutely love this for the both of you.
On the otherside of the spectrum, I think straight guys fantasize about doing whats most taboo to them, it's the shock and thrill of doing something they wouldn't do themselves, never tried, or had secret thoughts about. And the thrill only increases with a Domme telling them they have to!
I have to agree with this for the most part, although for myself I actually don't fantasize about things that are taboo to me. But, some of the most amazing experiences I have had is being forced to do taboo things by a Domme, so I do fantasize about the Domme forcing something rather than it just adding to an activity on my limits list. As for gay stuff, I am not scared of cock, I just have no attraction to or desire for other men in general.
There was an interesting thread years ago on Max (but it may have been posted here as well because certain people would cross-post like that) asking if you were forced to choose, would you suck a cock or kiss a guys feet & it was 50/50 on the answers. Personally, I chose cock in that scenario.