Harry told Top of the Pops magazine (via UnrealityTV): "I was on my friend's street and the girl who lived next door said she'd teach me a magic trick." He explained, "She told me to close my eyes and put my hands on my head, but as I did it, she pulled my trousers and pants down in the middle of the street."
OMG, that is so funny! Being the pranksters that the 1D guys are, we have no doubt Harry appreciated the pants prank, even if it did leave him...ahem...exposed in the middle of the street.
Niall's moment wasn't quite so awkward for himself as it was for a friend, as he explained, "At primary school, I used to try and make my friend laugh during class. One day he laughed so much, he ran up to the front of the classroom with wee running down his leg!"
via Source
