Ok, the funniest map to make* is this, loads of fun**... ready? make a zombie stooting gallery using lots of clip brushes, and trigger_pushes. -include levels so that when certain zombies are killed, new trigger pushes are added to the already existing ones, making them move faster, and have monstermakers drop ammo and weapons on the player, so he has a limitless supply... Make it into a mod so you can give the zombies custom sounds... Reskin the zombies so they look like clowns... etc etc...
The people are becoming restless! we need another compo!
*may not be the funniest map to make **may be fun only for non-specific period of time