One of my favorite things (rolling my eyes here, mmmkay?) is when I sub in for a prof who has absolutely no control over his class or lab. I especially enjoy telling someone else's student "no, really. Cell phone away. Now." And then be informed by the reprimanded student that "Prof. X, like, totally lets us text in class."
Oh, and I really like subbing for someone else who informs me, "good luck. They're really awful." Riiiiight.
But seriously, my favorite thing is spending an hour with someone else's supposedly out-of-control students, setting limits for the students, refusing to take any crap, and ultimately receive their respect and attention.
Suck it, suckers.