Why do some men think it is ok to grope a woman they don't know?

I don't mind it if it's in the correct setting and way. Like dancing in a crowded club and the guy starts dancing with me, and getting touchy. It's kind of hot. Sometimes maybe some guys pass through the club crowd and it's so packed that it "almost can't be helped" but you know they did it intentionally... that's also okay if it's just a little touch or grope on my ass or my breasts. Maybe I smile back or if they are handsome I will grab them and dance with them. Or at a bar, maybe having a drink and flirting, if I am in the good mood he can grope all he wants. I also often feel some men behind me in crowded places like the subway or bus. Most times they really can't help it and apologise. It's kind of cute. I don't mind making the day of some poor guy going to work... so guilty but I do play a bit by pushing with my ass against them and feeling them a bit. It's all a concenting game till I or they get off the next stop. But of course I am not talking somebody using force and trying to touch me deeper out of nowhere. Most importantly, because I let somebody grope me or kiss me, doesn't mean I am down for more.
If it's somebody I dated or my husband I don't mind them groping me even in public. To some might feel like they don't respect me... To me it means they enjoy being with me and appriciate me.