The sort of ones that pop into your mind decades later and you still stop dead and think “Oh god!”
Mine was when me and my sister were aged about 10 and 8. We were young, innocent and firmly into toilet humour/funny body parts. Evidently, we thought it would be hilarious to make our (pretty straight-laced) grandma a hand made card which harked “HAPPY WILLY DAY” emblazoned on the front surrounded by some pretty terrible drawings… you get the idea. I still remember the initial smile on her face when we handed it to her in a cute envelope, which immediately sunk to a stern frown when she pulled the card out of the envelope!
Argh!