Everywhere, in principle, it's the same.
Many, when losing, become enraged, shout about overpowered units, or "it was just luck," and so on, and, strangely enough, foreigners are often the ones doing this.
It's impossible, lengthy, pointless, and unrewarding to try to prove anything.
Sometimes, it's best to just stay silent. Often, this only irritates the opponent even more. And that's fine. We need to conserve our nerve cells; it's not easy to restore them.
If you can't restrain yourself, you can respond with something mockingly condescending... but under no circumstances should you resort to a vulgar exchange. Because then the opponent will achieve his goal – he will spoil the victorious triumph.
Even when I lose, I always thank my opponent for the game, if, of course, he was also polite. After all, there might be an Abram from the village of Pereperdyailovka on the other end of the line, and he's just having a bad day... we need to be more tolerant. Or more condescending.