Your opponent forgets to press his clock

As I understand it, you shouldn't speak to your opponent in tournament chess unless you are offering a draw or resigning. I have seen some pretty ugly situations where a player mentioned to an opponent that they had to hit the clock with the hand they touch the piece with. The proper thing is to call a TD - in this case, the opponent blundered after having his opponent complain to about the clock thing. 

Either way, if it is someone I like, I will just look at the clock until my opponent realizes they forgot. If I dislike them, I will just use their time to think or even get up and get a glass of water- as they may do the same...

If you live to regret it I bet you wont warn the next opponent!

Funny you should mention this, I remember the same thoughts and feelings in an OTB tournament. My will told me to inform him, it is the polite and kindhearted thing Peter Leko would do. But as I wanted to start moving my lips to inform my opponent this, a different feeling in my stomach told me, this is a rated tournament and your playing for a top prize. So I walked off and had lunch, a good half hour later when I returned my opponent had just realized he forgot to press his clock, and easily lost pushing 20 moves in 3 minutes. I would quickly inform this misake in an unrated or friendly game, not when there is something on the line. The judges count points on the paper, not generosity. Lets ____ in one hand while we with in the other huh guys?

Agreed. The first time it happens, I'll wait a few seconds to see if they remember, then point to the clock. They're on their own after that.

I tell them and appreciate the courtesy if I forget. I prefer the game to be decided on the board, not the clock. There is not much pleasure in a win when the clock decided the game.

I love that line!

I had a regular study partner and we played heaps of clock games from blitz to slow.

He constantly was forgetting to hit his clock and I dutifully reminded him all the time.

Eventually I tired of that and stopped reminding him. He didn't stop forgetting but at least his problem stopped becoming mine (and I just used the time to study the board).