I don't think there should be any embarrassment in sharing your fantasies with your partner. I never had such problem with my ex and he didn't have it either. Part of being in a relationship is about sharing whatever you desire, judgement isn't what makes a relationship healthy.
Well, let's hear your fantasy. I'd have to love a guy a lot before I'd play "glass bottom boat" with him. Then again, if he wanted me to dress up like the Queen of Sheba, I'd be uncomfortable but I'd do it for him.
Interesting question. I think most guys might be concerned if their fantasy was way outside of the accepted norm and if so, would want to ensure their partner was OK with something unorthodox. You should have a good feeling on your partner and open communications with him so you can discuss things like this without judgement. You also must be ready and willing to accept his response without judgement and then figure whether that fantasy is really worth pursuing in some way.