My favorite one has to be Posadism. You just want to obliterate capitalism out of existence with nukes and then pretend no one will die from radiation poisoning in the process.
Shitty game idea #234050: ACHTUNG! TL;DR
A macroscale RTS/4X Game alt-history game revolving around the Nazi's conquering all of Europe and remaining a superpower for 90 years. During this time, you will have to compete with Soviet guerillas in Siberia, a functioning and vengeful America, the...
WH40K Darktide is an upcoming co-op FPS similar in the vein to the Killing Floor, L4D, etc, etc, etc, but with a 40 gay paint, which makes it even cooler.
Here's my WH40K idea:
You play as a newly initiated Chaos Space Marine of the Black Legion during the 10th Black Crusade. It is a third person game similar in the vein of Space Marine and you get to choose which Chaos God you are dedicated to.