Back when I worked for a game publisher I really enjoyed taking totally ludicrous game ideas (or just names for games) and trying to make a functional game concept out of them. I'm not sure it's really a good idea to actually make those games, but it's fun to think about. A couple examples were a BBQ game, a bartending game, and one called "rock fight". The "rock fight" one is particularly funny.
The story goes that way back in the heyday of Atari, when they were pumping out success after success, the marketing department wanted to get in on the action. So they got together and came up with a list of like 7 "game concepts" that they then gave to the development department to make into games. Except what they gave them was just a list of titles - no concepts, just names - and the names were really, really bad... like "Rock Fight" and "Laser Gun". Yes, they expected the development department to make a marketable, successful game starting with "Laser Gun".
Now I don't know if the story is true - it was told to me by some co-workers who had been in the business a while - but judging by my own experiences with marketing in places like that I would not be a bit surprised.
But I took it as a challenge. I liked the idea of taking a ridiculous game concept and trying to build a game out of it. So what I came up with was an RTS where rocks are the only resource - they are both currency and weapon and raw material. You find rocks around the map, different rocks in different places. You can buy things with rocks, build things with rocks, and use rocks as weapons. Of course different rocks (conglomerate, shale, marble, limestone, granite, etc.) have different qualities and are more or less valuable and better or worse for different purposes. You are not told ahead of time what is what so you have to guess and experiment. Also different combinations of rocks can create different products. Using one rock with an obsidian might allow you to make sharp objects, for example. Using another rock type to grind others would give you blinding powder, etc.
So, Rock Fight. Let's make it!