The game should let you swear

I don't see what's the big deal in letting you write something like "lucky bastard", to a player who just stole a totally winning game from you because of time trouble.
Believe me, He won't be hurt - He just stole 12 points out of nothing.
It will only allow the loser to at least get some frustration out, instead of getting even more pissed by receiving that warning message. 

Maybe, sir, you should think about cleaning up your language instead of being "pissed" because you failed to manage your time. Take responsibility for your own actions instead of blaming the other guy for winning. After all, time control is part of the game, is it not?

If you run out of time, that's your fault, not his. Swear at yourself, or even better don't swear at all. It accomplishes nothing.

The rules of the game are the rules. Time controls, stalemates, harrassing queen checks, blunders, etc. are all part of the game. The only thing that counts is winning the game.

If your opponent wins the game, that's it. There's no need to swear at anyone to emphasize your frustration. If you have emotions you need to vent, put a punching bag next to your computer. At least you'll get some exercise while you play.

Not being able to control oneself is one factor that helps a player to throw away a game, swearing just increases a person's tendency to fail to control themself.

All wins in Chess come from being fortunate enough to either have an opponent who makes worse moves than you, or fails to control their clock in a game that they knew was timed when they decided to play it.

@OriSagiv

I have had that discussion like a thousand times here. There is no point in trying to convince them, since they already shiver with fear when they hear the simple f word. So we better not startle them 

So the only solution I have for you is this.

If you were going to run out of time and this chap was going to keep checking you to run down the clock, maybe you could have offered a draw?

Common people like us are not supposed to play chess. It's for the most polite people in the world, who have perfect speech. The chat function is for saying things like

"Good golly sire, you have been the benefactor of wonderful luck! I must congratulate you on winning a game you appeared destined to lose. Hip hip hooray sire!"

What I do is precisely swearing - but against myself. That's what you should do. I'm able to swear for one hour without saying the same insult twice. But of course I don't feel the need of typing it. 

And, btw, when you drop a wallet you can't tell it was stolen. Think about it.

You think it's luck that you mismanaged your clock and he didn't?

There are plenty of times in which my opponent is losing on time and I'll throw in an unexpected rook sacrifice just because it will take him an extra few seconds to realize that he has to capture and that eats up half of his remaining time and I can survive whatever he has left with his remaining time.

It's a private site so Erik gets to run it anyway he wants.  I think we all know this isn't really a family friendly site, but he wants to at least keep it from devolving.  I swear, I swear a lot, I even swear around casual friends, but I don't type it. I jump up from my chair, make rude (and occasionally inventive) body gestures to the monitor, curse every generation of someone's family and thoroughly exhaust my rage in a string of ever less likely expletives.  I'm not saying it's pretty to watch, but it's over and done with.  Anyway that's how I handle it. Maybe it's mostly a generational thing?  

If you can't handle losing, you shouldn't play. (Unless, of course, you are ranked #1 in the world, which you don't seem to be.)

I don't swear because He said you shouldn't.

Same thing happens in a friendly game with yer mates.

If you said what you said to their face, no probs.

But if you write it down on a piece of paper and show them!!! whole nudder ball game.

They should do that now, tbh.

And it looks like they do 

Is like Big Bruvva is always dey.

www.youtube.com/watch?v=5T9APeOD7Z8

So you're saying that maybe I shouldn't subject the Public Library to my tirades?  

I worked with a guy that could do that. His tirades remain to this day, the finest cussing I've ever heard. Occasionally when things go sour on the job, I'll fire off a rant, and think "Man, Don would almost have been impressed with that one!" Sounds like you and baddog are right there with him!