When I teach (TA, granted)... I don't make it about them. If it's about them, they can argue. I make it about me. :) It annoys me, and you'll be asked to leave OR I'm going to stop the lecture and start filming you &/or get other people to start filming you and providing the voiceovers. It doesn't matter what you're ACTUALLY doing... if you LOOK like you're snogging, glomming, having sex, whatever... it distracts me. So I'm either going to remove the distraction or have fun with it.
I have a whole list of warnings at the beginning of the quarter (including things like: if your phone goes off I WILL answer it and start talking with whomever is calling/texting, PLEASE leave it on! Unfortunately, it gets around rather quickly that I'm serious about this, so phones are off in my class except for people who arrange ahead of time for emergency types).
Mostly the series of warnings is an icebreaker on syllabus day, but I'm quite serious about them.
I avoid any problems with booting people by not requiring attendance.