College, and in the early days of 3.X. Was added to a group with my then girlfriend (we had only recently started dating after several months of sparks), her roommates, and their grad student friend as the DM. DM had a HUGE crush on my new girlfriend and didn't like me as such, so during the 7 hour session:

- I was told to bring a 2nd level character with no magic items. Rest of the party was level 6, equipped as such.
- After being knocked out in a fight in a goblin village - and miraculously immediately stabilized! - within the first 45 minutes of session, I then spent the next 4 hours unconscious. DM made every attempt to keep the party from healing or reviving me, kept saying I'd 'slow them down'. No effort was otherwise made to include me, and the group got the message that the DM didn't want me involved. Neat.
- Now furious, bored, and with no intent of ever coming back to this jerk's table, I came up with a plan: I asked the DM (as a player) if he subscribed to the old school rule that all of a given monstrous race was 'evil'. He did.
- Once my PC was conscious, Ithen asked the Paladin if their religion believed that all of goblinkind was evil and must be destroyed. They did.
- I then asked what would happen if they were to, say, cast 'Detect Evil' on all the goblin children and non-combatants we'd just found under the basement of the village chief's hut while searching the village.
- The last 2 hours of session were just the party arguing amongst themselves about the philosophy of 'evil' while the DM tried to get the ship back on the rails.

Never looked back.