I answered this question from Brianna in Yahoo! Answers this afternoon:
Just a Quick Question?
Okay so im in art and we was painting so me and my friend was washing off the paint brushes and we were playing with the pain brushes or watever and this guy i know pulls me by my back pockets if my pants and nodds his head up. (saying sup) why did he do that?
Maybe he wants to play with your brush.