You can not get pregnant by setting your clothing on fire.
In fact, have no idea why someone might think you could get pregnant this way. Maybe they’d been watching too much science fiction and were imagining semen infested smoke curling up from a young man’s soiled pants and entering the womb of his lover?
Hmm… if I sold that plot to the right hentai director I bet I could make millions!
Explanation for why I’m bringing this up
Someone asked me if it was possible to get pregnant by pants burning. I suspect they mean dry humping, which we’ve already covered, but I am not completely certain. I suppose someone could think that “hot” sex involves fire…