Okay, I have NEVER told anyone this in RL.
When I was in primary school, aged about 8/9 I used to pick my nose in the girls toilets and wipe it on the wall (oh the shame). I don't know why i did it, but I did and never really thought anything of it.
Until...the very strict Headmaster of my RC school held a special assembly in which he was furiously shaking as he discussed the "nose dirt" problem in the girls toilets. He kept talking about it for ages and constantly referred to it as "nose dirt".
I was so terrified they would know it was me just by looking at my face I nearly wee'd myself 
I've never done it since 
I've never eaten my bogeys though (retch) although on occasion I have caught dh doing so (usually in the car) and bollock him for it, though he denied it vehemently (I had something in my teeth etc 