Like Sit-Com, Sit-Hom is a situation homosexual. A man who is normally straight but, given the right circumstances, might be persuaded to go for a bit of man on man.
Hey Billy, did you know Mike went to Quentin's party last night? He has a regular bird but I reckon he might well be a Sit-Hom given the chance. Quentin's certainly smiling this morning.
Like Sit-com a sit-hom is a 'situation homosexual'. A normally straight guy who might take a chance at gay sex given the right circumstances. e.g. at a drugs or drink party.
I reckon Mike swings both ways. He fancies a lot of girls but I reckon at a drugs party he could well be a sit-hom.