Not to worry, these situations don't come up for me in real life.
I will make one further observation, I'm not yet convinced that no thought process is involved. After all, one's hand can cause arousal, but thought is needed, I doubt if any of us become aroused while showering or going to the bathroom.
I would be interested in learning how the heterosexual gay porn actors do it. Do they think about women while performing? In your mouth example, if my eyes were closed and I mistakenly believed a female was involved, certainly I could become aroused. If I knew a male was involved, and I wasn't, say, pretending it was a female, I doubt it.