It was back when I was 18. I've always had an interest in that sort of stuff so I made myself a decent sized batch of anfo. Then me and a mate carried it down the road and put it in the corner of the local hotel garden - they were posh used to hold loads of firework parties and annoy the residents (us) so I figured I'd give them some payback.
Trouble was I got my maths a bit wrong. Instead of making a bit of a bang it was huge. They found the lid of the box it was in about 250 yards away and there was a hole in the lawn big enough to bury a washing machine in!
Here's a youtube video I found of 16kg of it going off. I recon that's about the size of the one I made, although I didn't weigh it.
Edit... The police called out the EOD. It took me over a year with two visits to crown court to talk myself out of it. Ended up doing 120hrs of community service which was a result. I nearly went down for it.