Yep, you got it. Anything and everything goes. Any fandom, any pairing, any crossover, any prompt. Leave your inhibitions at the door.
Just make sure to be nice to the codemonkeys by leaving your prompts in the proper format. Otherwise, they may pelt you with bananas. ;)
For a single fandom: Fandom, Pairing, Prompt
Example: CW RPS, Jeff/Misha, "please"
For a crossover: Fandom/Fandom, Pairing, Prompt
Example: Lotrips/CW RPS, Harry/JDM, glow
Don't forget that we have a lot of lonely prompts lying around over here, so if you can't find something you like today, feel free to go give them some love!
Now go wild and have fun!