Steps;
1) Chop like.. loads of wood. You can do it basicly in any town or village, all you need is a Woodcutter's Axe. Chop, chop, chop. Like 100~~.
2) Go somewhere near bandits, and unload all of the wood you have.
3) Make a 5x5 yards wide surface with it, and cover all of the holes with wood.
4) Shoot one of them bandits, and stand behind your piles of wood.
5) Once the bandit/bandits step on it, blast it with firebolt or anything that causes explosion. Together with piles of wood, bandits will get blowed away with it. They will fly really nice and get one shotted.
6) Gloat over their misfortune.
I am so sorry for not being able to record it, since I am on xbox, but I promise to those who actually want to try this out, yes it does work and it looks funny. Maybe it even works for other mobs like giants or mammoths.. Haven't tried it out yet, but I will let you know if I do.

There it is, trap some people have been wanting so much.