It seemed like he was trying to go all or nothing with showing his weirdness/fucked-up-ness. Didn't he do a really similar thing to Hannah back in Season 1, crawling and all? She was pretty uncomfortable with some of his weirder kinks, but those scenes weren't nearly as unsettling as this one.

I don't think she actually said no or told him to stop, just to not ejaculate on her dress.