I was playing around on some stages and i found some pretty funny exploits while playing some stages.
On Gravel Pit in the Blue Base there are two I found. One being able to jump onto the gate to the right of the entrance and one being stuck between the Right electric pole the wall and the entrance. When we lost I was on the gate and the demo who came in just laughed at me.
Gold Rush has one on each stage.
The first one is that ledge on the left side going to the blue base. On the next stage there is a small ledge where you can jump up to and demo camp. On the last just like the first there is a house. The enemy engineer saw me and didn't even try to attack me, he just stared.
On Granary if jump off a Crit. Mine you can jump all the way above the stage and get stuck up against the wall on the third floor.
I also did some demo camping on some custom stages.
I would have a screenshot of these floating sticky mines but my brother decided not to exit the game correctly when I left to do a chore and they were not saved.