I've only been in a tiny handful of actively bad games. If the group is good, problems can be worked around and resolved before the next session -- and I've been lucky to fall in with some damn good groups.
But when I was working at the newspaper with a huge number of non-geeks, I lived in the middle of nowhere and my roommates had no interest in tabletop gaming ... out of desperation, I accepted an invitation to an irregular game that one of my coworkers played in. I showed up at the spotless and largely empty house (I know, I should have run screaming right then and there), sat down, rolled up an AD&D character (IIRC, 3rd Edition), and started to get a sinking feeling when I realized that our gamemaster was using a monster manual as the entirety of his adventure notes.
For no explicable reason (not even "you all meet in a tavern"), everyone gathered at the dungeon, which was an abandoned mine, and we gave marching order and wandered in. A sample interaction, recorded as faithfully as memory will allow:
"Alright," the GM asks, "the corridor you're walking down splits into two. Do you go left or right?"
"Uhh ... I dunno, are there more footprints going down one of the passages?"
"No, not really."
"Are the walls different? Is there any light down either of them? Is there anything at the intersection?"
(The players all look at each other; finally someone speaks up)
"Um, we'll go right."
"Okay," the GM says. "You continue down the passageway. It starts sloping slightly downward. As you continue walking, water rises around your feet. You look down the tunnel and realize it goes totally into the water." (Naturally, none of the characters has any sort of water-breathing gear.)
"... Um, okay, we back up and go left."
"Alright. You walk for a while, and then the passageway splits into two again. Do you go left or right?"
Finally, after four or five Y-junctions, we reach the first sign that these tunnels have a purpose: a slightly wider room with a couple of exits, and (gasp) a coatrack with some of the miners' coats!!!11!
My face lights up. Finally, after enduring the tedium of a "Detective"-quality pathfinding game, something in the environment to interact with! Maybe we can find out where all the miners have gone or why we're here. It makes no sense to put your coatrack several miles into the mountain, but never mind that: finally we can start gaming. "Alright," I say, grabbing my d20 and double-checking my thief's skill load one more time, "I'm going to examine the coats, first checking the pockets. My search roll is --"
"What's your AC?"
"Does a 17 hit you?"
"Uh," I say, thrown, "yes?"
"Alright, the cloaker hits, take 11 damage. Everyone roll initiative."
I try to say "..." but what comes out is one of those vanish-marks that looks like an asterisk with the guts removed.
The party mops up the monster with minor hit point loss.
"Good job," the GM says, and consults the rewards table in the Dungeon Master's Guide. "Everyone gets 300 experience points. Which exit do you take from the room?"
At that point, I think my brain cast Cause Serious Wounds on itself in order to inhibit memory formation. The only other thing I remember is walking from one of the mine tunnels into a gigantic and inexplicable natural cavern, where we fought off a shrieker (the living stalactite monster) and a bunch of stirges (bloodsucking flying things). At some point there was a token trap, which of course got immediately set off by someone other than, y'know, me, the thief, because I wasn't first in the marching order.
The coworker who invited me to game noticed the trauma on my face the next day and wisely never spoke of the experience again.
It took several years for my dice to forgive me.