When I was 5 or 6 years old: embarrassing story win -
Me and family were just watching TV when I suddenly stood up and farted. I started laughing, everyone else followed. Then I just stop laughing and run away crying - they were confused and thought 'why is he upset, was it because we laughed at him?'. What actually happened was that I followed through horrid and mother had to help clean up my pants.
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On the school bus, and I tried to make a friend feel really awkward. He was sitting next to a girl I knew he was fairly interested in, but I didn't know much about her myself. We were all talking about a party we were going to when the girl says "Yeah I'm bringing some wine. I get so drunk so quick on it, only takes half a bottle"
To which I say "*Dan's taken note"
Then I get a look from him as if he didn't understand, and the girl is just confused by the social violation and ignores me and just speaks to Dan "is he trying to be cheeky?" to which Dan says "I don't know, I didn't know what he said"
Then there was an awkward silence as I was left cringing at the situation. My friend later told me that he actually found the comment funny but just denied all knowledge during the situation.
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A few years ago: I pulled my sister's chair from her as she was about to sit down. She obviously fell down and I started laughing. However, there was a nasty sort of, I dunno, a clicking sound. Whilst I chuckled, noone had joined me (there were a few families round for a barbecue) and they just stared at me. That was when I remembered that she had a back problem.
I'm pretty sure there are more embarrassing moments I've forgotten about, so I'll come back when I've remembered some.