I think for me it was back in college where I thought it would be funny to laugh at someone in my class for not being able to read/speak English or French.
The class froze and the girl answers back to me saying "It is not funny"
I kindly said sorry but she hated me.
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I asked for help, from a Russian, on how to beat one of the call of duty games. I believe it was MW3. Anyway, he didn't look too happy after I asked him.