Building TNT traps in minecraft to troll people can be so fun. I've wasted about 2 days just Making destroy their own bases and stuff. 

Tree bombs that blows up whoever chops a block from it. While they look around for a creeper... Boom.

Even rigged a random tree out in the jungle. I should start a pool to see how long before some poor unlucky bastard out on an adventure runs into that tree bomb in the middle of nowhere.