I sometimes play on a survival server where griefing is not only allowed, but almost encouraged. Keeping yourself safe and other on their toes is important. :)
So, I came up with this simple TNT + pressure plate trap.
I know what you are all thinking at the moment. "Aaaw, not THAT old trick." And no, it isn't.
Well, the base is the old TNT, sand, and plate trap. That never works because no one steps on random plates in the desert. Even if they did, they wouldn't stay long enough to be blown up. So we need to add something.
Ta-da! A house. Since a pressure plate in front of a door doesn't raise as much suspicion as one laying around in the wild. But since people still will walk right through the door and escape the TNT explosion, we need to be a bit sneaky.
When placing the door, we "hug" the right wall like this:
Which will make the door to be open when the plate is idle, and closed as soon as someone steps on it.
Just close the door by hand when you are done building, stay away from the pressure plate and the automatic door opening that people will expect is replaced by a fall and fizzing TNT.