Because the people who feel the need to do so are either...
A) Hormonal teenagers or perpetual losers without the interpersonal skills to communicate with the fairer sex in any way more delicate than perhaps mumbling incoherently while staring at their own feet.
or...
B) Mentally deficient asshats who want to push the boundaries of decency, just to see how far they can go before a mature person finally tells them where to stop. These are the kind of people who run into trouble when they are forced by their parents to finally get out of the basement and engage with the real world.