Mocking someone for mispronuncing a word is a jerk move no matter the circumstances; unless, maybe, it’s a good friend and you do it in a gentle teasing kind of way. But ridiculing someone’s pronunciation when it’s their second, third, or Xth language, especially when you’re monolingual yourself, is definitely not right.
Yet that’s exactly what happened to this redditor. Being trilingual himself, the OP was mocked by his American friend for the way he pronounced a word in English. But the mocking didn’t last long, after the redditor clapped back at said friend.