Do guys usally grope their female friends as a joke?

My friend's brother has been really touchy feely with me lately. He's engaged and has a baby. Whenever his fiance isn't around he'll touch me in some way. Sometimes he just puts his hand on my back, but he has also put his head against my chest, stroked my legs, and smacked me on the ***. He's said some pretty graphic stuff to me too. I talked to another one of my friends who's known him for a while, and she said not too worry about it and that he's just kidding. Is that at all normal? Should I just take it as a joke?