When I was 17, I had a bit of a stupid (understatement!) moment...
I bought a new drivers seat for my Audi A4, but I didn't have enough room in the car to put it in, so I took out the drivers seat and drove to collect it sat on a bucket. Got pulled over by the police about a mile from home and the officer was a mixture of bemused and furious. My passenger walked home, tied my old drivers seat on to the roof of his micra and drove it back to me. The officer then watched us fit the seat and let us carry on with nothing but a strong word of advice. During my 40 minute dressing down some of the questions I had to answer were:
1) Why didn't I take the passenger seat out instead - I didn't want to hurt my friend if we crashed (obviously not thinking how we were a billionty times more likely to crash with me perched on an upturned bucket!)
2) Why didn't I just put the seat on the roof of the micra in the first place - it was a seat for an audi, so we naturally thought to take the audi (pure idiotness!)
3) Why we thought driving three miles sat on a bucket was a good idea in the first place (it wasn't!)
4) Did I really think that a seat belt would do anything if I became a projectile inside the car (it wouldn't!)
He didn't prohibit the vehicle from use as I fixed the defect there and then, but I did get a few "random" stop and searches for a couple of months
Let's just say, lesson well and truly learned