Kid, I am standing behind you while giving the lecture on how to use the library catalog. As such, I can see you playing online ping-pong, looking at ESPN, and basically doing everything but paying attention to me. When I call you out on it, switching over to dicking around with your phone isn't exactly subtle, nor is falling asleep.
I am not saying these things for my health or my own edification. Do it again next week, and I'm going to use the NetOp software to display your screen on the projector at the front of the room. Hope you're writing a totally inappropriate email to your girl when I do it.