How do you assert boundaries without these pieces of trash expecting a refund?

It feels quite dangerous at times with some of these men expecting a refund because it doesn’t feel like “REAL sex with their girlfriend”… But these men are usually terrible in bed, slobber you like a dog, somehow accidentally bite you… somehow yank your piercings… attempt to bend you in awful uncomfortable positions… touch my tied up hair with their disgusting wank hands.. or throwing their clothes ontop of or too close to mine…

I know I have to work on my boundaries and asserting them, but it becomes SOOO TIRING when they just don’t listen and I become mentally exhausted.