you get checkmated in 0 moves
The rage moment when....
When you are checkmated with your opponent having 0.1 seconds on the clock (see the masterpiece ChessNetwork vs Wolfman for details)

When your opponent makes you laugh whitch makes your arm go sideways knocking down a cup of wine on you computer then suddenly combusts into eletric shockways shocking you to death.

When you have the game won in about 11-15 moves.
Your opponent will rage to resist being checkmated. You will counter with rage to mate him/her with force. They will counter your counter rage and meet force with force and evasive King maneuvers.
Then you mate and jump up say i took you down hard! Now the question is will either party say gg?

When you see your opponent's silly cheapo, get lost in thought over something much more complicated, glance at the clock, panic, and forget about his threat...
Which of course he then plays with an air of smugness detectable from thousands of miles away.

When im about to win and blunder and get mated in one , >_>
When your opponent responds with lol and will not give you a rematch!

When you are winning positionally, have more material, have more time than your opponent on the clock, have an excellent connection and then somehow are given the loss "on time" even though you had more time and an excellent connection.
That is probably the only thing that contributes to a rage moment for me.
But then I get over it and comfort myself knowing that I'm actually better than the record and rating shows because some of the losses were when I was winning.
And then I have a good laugh at myself for even almost caring about the results of a digital boardgame in the first place.

....you caught your opponent in one of your favorite openings and just pound on him for 20-25 moves until it gets to a point where it's so easy that there's no need to calculate, but your opponent doesn't get the memo and does calculate, and the clever mate hits you like a round-house kick to the head, and you realize "I'm going to sleep now."
You checkmate your oppoment in 3 moves