How many times should I let my opponent know they forgot to press their clock? I've had this question on my mind for a while, and I searched around and found a previous question (Should you let your opponent know if they have forgotten to press their clock?) that touched on the subject.  In that previous question, it was asked if one should remind one's opponent if they forget to press their clock.  The general consensus in the answers seemed to be, yes, remind them - and I always have done so, myself.  My question, though, is - at what point do you stop?  I've played against a number of opponents who've had the habit of forgetting to press the clock after almost every move.  After reminding them the third or fourth time, it starts to get annoying, and it distracts from my own concentration on the game if I have to continually watch to make sure my opponent deals with their clock as they're supposed to.  At what point does one just give up, and sit there and let their clock run until they figure it out?  At what point is it no longer poor sportsmanship to refrain from warning them?  If I've already reminded someone four times in one game to press their clock, does it make me a bad sport if I just sit there without speaking (or gesturing towards the clock, which is what I normally do) and without making a move, and let their clock run out when they do it the fifth time?

And actually, now that I'm thinking about it - am I actually committing a rules infraction myself, by communicating with my opponent so frequently about their clock?  I've always wondered about that, too.
Its a matter of opinion, and much more likely to occur at the beginner or amateur levels of chess.

I believe it is best to show the high levels of sportsmanship and notify them immediately for the first couple of times they forget to press there clock.
If they continue to forget to press the clock, start by waiting 1 minute, followed by 2 and 3 etc. … If it's becoming a serious problem and your position (clock and board) is sufficient, I would consider going for a walk to look at other games in attempt to drill the point home.

Drilling deeper into the matter, when players don't press their clock, they are costing yourself and themselves XX seconds from increments and can cause problems when playing games with multi time control periods.