my pet peeve is when people finish using a program, then close the window but do not quit the application, and then leave the computer like this for someone else to come and start yet another program and do the same thing until all the apps on the computer are running , and something happens and then i got to fix it, and they say "hey, what's wrong with this thing?" ... or they double on a program that is already running, with no window open and they think nothing is happening.