Some of the worst games I've been in where ran by a specific person who is no longer part of our group because no one can stand him.
He was prone to handing out unearned treasure and minor artifacts just because. We had two or three adventures where we would go in a cave, fight 20-50 goblinoids, and find a 1 million gp diamond or something else. We carry it out, sell it, end of adventure.
Another game, I had the misfortune to want to get healed, and instead of getting healed, I was mind controlled and teleported to the mayors office and forced upon the job. No save on the teleport, and even though I had spell resistance, he rolled it, failed it, and said "He makes it!" He gave me this frustrated and annoyed look.
It gets worse.
So we all meet in this tavern, and when the female players have their female characters walk in, the bartender says no wenches in the bar and points to this sign saying "No Wenches". Wtf?! This is the kicker - when the females leave, the bartender leaves, a new one takes his place, and takes the sign down.
We all eventually go to this abandoned temple, in part because of me (I was mind controlled), and when we entered, there was a trap. Well, some made it and some failed. But I was playing a drow assassin (just don't ask) and I had amazing saves but I failed, so the DM rubbed it in my face. One player and the DM argued for an HOUR because the player pointed out that the trap could never work mechanically and the DM couldn't justify it because his explanations were weak.
This next event requires a little explaining. One of my friends had a sentient hammer. Jokingly, he asked the DM if it could fly and pull him around like Thor's Hammer does in the comics. The DM says no. Fair enough.
After the trap, the two female characters decided this sucked, and they would rather be somewhere else. So they try to leave. The DM calls for a save from my friend with the hammer. He fails. The DM says the Hammer starts flying and pulls him along. The Hammer pulls him in front of the path of the two female characters and forces my friend to threaten them to stay in the Dungeon or die. Obviously my friend doesn't want to do it, but the DM forces him to through the hammer.
Eventually we get to the center of this temple, and there is one person in here, the last worshipper of some gem god. We kill him and take the treasure, which sure enough, is over 1 million GP in gems.
Needless to say, that game left a bad taste in our mouths.
EDIT: Ah yes, I forgot to mention this little gem. After the game, he asked us how it was. Since we were friends with him at the time, we didn't want to hurt him so we said it was okay. He looks at me and says, "Yeah, I like to use plot in my games." I don't know whether he meant that as a scathing remark to imply I didn't use plot, or whether he was deluded. I have never wanted to punch anyone in the face as much as I wanted to punch him right then.
But I don't think he has the Intelligence necessary to be able to make up subtext.