Mine was when I was with my grade five math teacher who i had a huge crush on, (MILF) and i was helping with her after school duties since i liked her, and she was complaining that her feet hurt, so i sat down with her to take a break, and i began to massage her feet, her feet were very big but very beautiful, and i was flirting with her but she didnt realize, then her glasses fell on the ground so i bent down to pick them up, and i geuss my pants came down really far and she saw about more than half of my undies, but even though i was 10, i was wearing my "Tellutubbies" tighty whities, now i DID like them, they just were ones i rarely wore, but they came in a pack with shit like power rangers and ninja turtles, shit i always wore, and unfortunatley all the ones i did like were in the wash, so there i was with my tellutubbies briefs right in front of my teacher who i liked, i was fucked. i got up not noticing and she said "umm arnt you a little old to be wearing those?" i asked what she meant and she said "your briefs have the tellutubbies on them, dont you think your a little old to be wearing underwear like that?" i was so embarrassed! i didnt even know what to say and i just stammered and said "well i dont like these ones! well i do like them, but theyre not my favs. i mean well i wanted to wear power rangers, but-- oh wait! i mean, well these are my only pair! well i actually have 3 but-- i mean--wait i---" it was awful! my teacher giggled and said "dont worry its no big deal, if you like wearing them thats fine" i just said "well ya i like wearing them but-- wait! i mean---" and i finally just ran home it was horrible and now that teacher still calls me "tellutubbies" luckily ive seen her undies alot over the years 2, so whenevr she calls me that i just say "granny panties!" that shuts her up 
XO X(
XO X(