Yes,it is concidered rude however in my opinion it isn't rude at all S and M is a sexual practice involving the inflicting of pain -- many people find that to be disgusting.
The song "SnM" by Rihanna is about having sex.. "Sticks and stones may break my bones but chains and whips excite me!" .. "I may be bad but I'm perfectly good at it, sex in the air, I don't care, I...