What's the name of this movie?

Theres a movie where a stupid guy goes to the library and meets this hot girl and she seems so innocent and she gives him a special book. Then they go to her house and he meets the grandma and then they go to her room that has a bunch of stuffed animals and junk and she uses her strong stuffed animal to tie his hands to the bed and she puts on a y black leather outfit and he is like oh ya baby. Then the bed comes apart and he is lifted and naked and then the wall behind the bed opens and there are a bunch of things to or whip with and the grandma comes out in a y leather outfit and he says oh **** and they whip his ***. Then later in the movie his other stupid friend says I met this girl at the library and she gave me this book and the dude from before says awww **** and runs. Then it goes to the part where the friend has to go through the same thing but he continues to say awww ya baby even when being smacked. What's this movie?