When I was about 5 years old, I stuck a small toy train deep into my nostril and couldn't pull it out by myself. Soon afterwards, I went to a hospital with my mother. :D
P.S. I thought of this topic thanks to Estanis's discussion "What's the craziest thing you've ever done for love?" and Rose's comment "I grew up with four siblings, and we often speak about our childhood. We laugh then about all the crazy things we did. "