The reason I am so pissed is that I work in a company where we do things and make jokes that would get you kicked out the door in most suit companies and everybody enjoys it -- including the girls (who are often the best) -- and yes there is the guy who doesn't find it funny to change his screen, so we don't. To him. If he finds it obnoxious that we make those jokes with others, he can deal with it or leave.
And yet, if somebody where to join us who would get annoyed working there do you suggest the rest of us should leave?
I wouldn't make the joke I did in a company that didn't appreciate it but I wouldn't stand for it being change just to fit a few people either.
But someday you may hire someone who, as it turns out, does not appreciate the jokes. Or perhaps, like Jessamyn, enjoys the jokes sometimes but feels that they are overdone to the point of being irritating.
I would not advice you to tell this person "If [you] find it obnoxious [... you can] deal with it or leave." Because in the US (I can't speak for other places) that is illegal. If this sort of behavior is pervasive it is said to "create a hostile (or offensive) work environment", and if someone is fired (or effectively forced to leave) because they do not enjoy the behavior then they are well within their rights to sue your company.
I'd also question your belief that "the girls" (who are, I take it, 8-12 years old) are ok with it. Go talk to some people in the field who have had a few jobs but aren't stereotypical. E.g., gay, female, or black. Ask them if they've ever laughed at something that made them uncomfortable because they wanted to fit in and felt unsafe doing anything else. Because you're ok with pushing out somebody if they don't like the joke, guess what: if they don't like the joke, they'll still pretend to you that they do.
Suppose you worked at my startup. Suppose further that you suggested to one of your colleagues, as you did now, that they quit because they weren't inclined to put up with what they saw as a hostile work environment. You know who would be gone? You.
Startups are a team sport. We don't require suits, because how somebody dresses won't change the quality of the product. However, driving off perfectly good people because they're different will definitely change the product. The same applies for a culture where people don't feel respected, or aren't encouraged to fix the problems they see.