So reading the book model, I encounter this chapter. Mark talks about how his natural friend said to girls "can i pee on your butt" and gets result and how he cant(during that time).

Mark said because he's looking for a reaction. Actually, looking at that, i think both of them looking for a reaction...but they're looking for a different reaction. Mark is looking for girls to like him for saying that while his natural friend was looking to annoy the girls for his own entertainment and ends up getting the girls as a biproduct(but was never the original intention). Both are reacting seeking, but one is attractive while the other one is not.

Thoughts?

His friend was ok with whatever response from the girls and "knew" that the girls reactions wouldn't mean anything about him. That's how I see it. Mark was only looking for the one reaction you've mentioned.

Dude, I know the guy pretty well. He wasn't looking for anything. He just thought it was hilarious. Self-amusement at its best (or worst).