I think my most embarrassing moment was when I was 14. I fancied a girl called Paula, and kept on pestering her. Anyway in the middle of a History class I stood up & Paula managed to creep up behind me and pull down both my pants and boxers before I had time to react. Everyone in the class saw everything, including the teacher.
I was so embarrassed, I was quite timid back then. Then all the lads in the class were teasing me by saying I had a 'stiffy', I did not I tried laughing at the banter, but got really uptight, and eventually ran out the classroom. At the time I can't explain my embarrassment.
The only plus point was Paula ran after me to apologise, and was nice to me for a few days, but then ignored me again. My friends at school never let me forget the incident.
Now over to you.............
I have other embarrassing moments but this is probably the cleanest!