My worst...in middle school my friend was running the game (I think he is the reason I avoid letting others DM). He came up with this wonderfully detailed empire called Thascanaria. Within it was a city so large that it made New York city look like a hamlet. All this with pre-renaissance technology. This vast city was mapped in great detail...but only he got to see the map and the lovely citizens of this magnificent capital had opted not to put up street signs or maps or allow guides or anything useful like that.
I once spent six (real) hours trying to get from a park to the inn where my fellow adventurer was staying.
But this is not even the worst.
This guy during the game had my old Monsterous Compendium, complete with universal encounter charts, which he used without concern for such trivial things as encounter level, relevance, plot, etc. On top of this there was really only one major plot for the entire world, a ancient lich madman who was trying to take over the world with the aid of his various minions, all of whom were more powerful than your average 20th level character (this in 2e mind you). We would meet them from time to time (or some dragon from the encounter chart) and procede to die painfully.
It got to the point where we would make books of characters so that we could just grab another to replace the oft killed ones. In the 3 months that allowed him to continue this travesty, I ended up playing 20 or 25 different characters. My older brother joined us 2 or 3 times and managed to go through 5 characters. My buddy who was also in the game went through nearly as many characters as I did (the DM liked him better).
Eventually I asked the DM what the point of the game was and what he hoped to accomplish by killing us ever session. He got mad and refused to run the game anymore.
Damn, I'm glad I never have to be in middle school again.
DC