Another issue just came to me. I had this one horror DM who did TPK on purpose because we ignored his plot rails (and he petulantly did it in the least fun way possible: some angry god just teleported us into a dungeon where we couldn't move or do anything, and tortured and killed everyone. So we didn't even get to have a battle or roll any dice, because that would have been too fun and we'd ruined his plot), and the other horror DMs who set the plot rails up to kills us if we followed them.
One guy had a room (literally the first room in the quest dungeon for a level 1 party) with like 3 goblins in it, we had 6 players, and decided we could take them, but the DM just kept pouring more goblins in as the first ones fell, they just didn't stop coming and the whole party went down. Oh right, I guess the true plot was that all the characters we'd just rolled up were meant to run away from literally the only place the DM had told us existed. I guess that's realistic: first level characters would be minced in a real goblin lair, but it's hardly a "game" at that point. It's the DM's job to create a story that's appropriate for the party, not to be lured in an ambushed by 4 times as many goblins as there are players. :/
EDIT: though I have an idea how to beat a DM like that in future. Make sure to buy some extra spears (they're cheap) or other weapons with a longer reach, then have everyone back into the doorway, if there's a door only one goblin can be standing in the doorway at once (only 5 foot wide), 3 fighters can stab into the doorway and other characters can stab with spears from 1 square back. If the tunnel is 10 foot, then two fighters with the best defense in front, two others with spears in back row attacking 2 goblins at a time.