Only fairly recently I experienced that, giving a kinky exam to a straight guy..when we talked about it, he said he only liked to play with women doctors, so I asked him if in real life his doctors were female. He laughed and said I was right, he did not see it before... actually just the all game of pretending, felt very exciting.... a little later he was naked in front of me, I had only checked his ears and was doing his neck that his erection was poking at my belly...had him dripping with the prostate check and when I suggested he needed an enema, he took it in stride, even if it was not in the cards.... took particular attention not to make him shoot.... When we had finished, he stood there, fully erect, looking at me waiting for something... I put an hand on his ball and told him the only thing left to do, was to take a semen sample...yes, doctor, if we need to.... he filled the little dish I had with just a few strokes....
After we were talking in front of a glass of wine. Asked me a lot of questions, he knew I was recently widowed, what was like to play like that with a "straight" guy...told him it made no difference, that was was important was the play, the fiction....he thought about it then kind od sheepishly, he asked if next time he could play the doctor. But of course. We became fast friends and we explored other kind of play too. Too bad he does not live close and he is married. Started training him to take my fist....
Of course not all the other straight guys I've met, end up that way. The great majority are usually kind of embarrassed in the beginning, warming up a little when the more invasive exams are performed. But never had a problem getting my sample... A few of them were more embarrassed afterward...