Bit risque, this one, but never mind. You can tell me if it offends you afterwards.
A teacher decides it would be a great idea if all the children did a project about their dads' jobs. To get them into the swing of it, she asks them to come in the next day dressed in their dads' work clothes.
Now, it happems that young Johnny's dad is a welder. So, next morning he puts on a pair of overalls and one of his dad's spare welding masks and sets off to walk to school. What a nightmare - he can't see a thing. He bumps into the gateposts as he's leaving the house, he bumps into people, he bumps into lamp posts and he bumps into the headmistress who's waiting for him at the school gates because he's late. Throughout the day he bumps into teachers, desks, walls - everything.
Come hometime, little Johnny feels his way out of the classroom and goes to catch his bus. Because he still can't see anything, he misses his bus and sets off on the walk home, still bumping into stuff. A car pulls up and the man inside offers Johnny a ride. Normally, he'd never think of accepting lifts from strange men, but today he's fed up with bumping into everything, so he gets into the car and they drive off. Almost immediately the man says: "little boy, do you know anything about homosexuality?" "No" replies Johnny. After a while, the man says "do you know anything about paedophilia?" and young Johnny says "no" again. The man tries again: "do you know anything about frottage?" "No" says Johnny, "and I should be honest with you, I'm actually not a welder at all."