I can get over almost all the little things that people do in league play but the blatant cheating is the thing that really really bothers me. Its not in every match, but in at least half of my matches I expect to get hooked at least 6 times. There really is nothing which can be done about it, so I have finally learned to just accept it and move on. If I get angry, I will lose at least a game due to it.
I guess I took 14 years off from tennis and this is the thing that changed the most. Back then, there weren't too many cheats but they were well known and in tournaments you just immediately got a line judge. I think the morality has changed because it almost seems like the people who call it clean now are the minority. The worst is when you know your partner cheats. I've corrected many bad calls in this case, but there are some you actually can't see.