> A rude gesture or crass words seems vulgar. A video of a penis being sucked doesn't. "Vulgar" is the sort of word you might hear a shrill, paternal sitcom character use to describe a minor inconvenience or faux pas, and it's just as hilarious when people use it as an argument in real life.
In the mean time you can spare people gratuitous, graphic descriptions of explicit sex acts, AKA pornography, and keep your depraved fantasies for yourself.