My list of pet peeves...
1. If you're riding with a partner, don't wait until your partner has completed his shot before you prepare for yours. If the balls are close, both partners need to be out of the cart and in their pre-shot routine. I can't tell you how many times I've watched one guy going through his routine while the other sits in the cart. After the shot and the club is put back in the bag, the cart drives to his cart mates ball 10...stinking...yards...away. Now you have to watch another guy go through his entire routine. Both golfers get out of the cart and get to your ball. Even if you are far apart, let your partner select his club and you take the cart to your ball and return to pick him up when you've hit.
2. I'm all for playing by the rules and counting every stroke. But if you are terrible, for the love of sanity, please take distance and a stroke on OB. It isn't by the book I know, but these guys aren't playing by the book anyway.
3. Like Duke mentioned, don't wait on your cart by the green adding your score. Look in the rear view mirror once in a while. There's as much world behind you as in front of you. Be aware.
4. For the love of sanity, please repair your ball marks. I literally repair two or three every time I get on a green. Un-repaired ball marks are why munis have greens in such disrepair. Some of the ball marks are literally within feet of the hole so no way they were forgotten or unseen. And please lift your feet on the green when you walk.
5. There's a million more.