Oh this is a fun one.
I was at my friends house when I was like eleven or something (about the same time I started to play videogames) and he was playing Unreal Tournament online talking to people through a headset. He spent like 10 minutes trying to explain to me how a microphone worked but I still acted like I had seen an UFO.
Finally he just handed me the mike and said "here, just say something". Completely baffled I said "Hej", meaning "Hello" in Swedish. My friend said "Nono silly, they're English, you can't speak to them in Swedish". So without thinking at all I put on a thick British accent and said "oh I see, would you like to have some tea". My friend just started laughing.
Not exactly my proudest moment in life, we still tend to joke about it x)