The guide, a Orc NPC, warns them not to go deeper as the places are unexplored and there are many dangers deeper, its also not part of their mission.
The player playing as the rogue insists on going down into the cave against the advice of the NPC, as there might be treasure down there. The rest of the part argues that they have more pressing business than going into a random dungeon but begrudgingly goes along with him. [...]
The orcs tell them that deeper, the ruins get weirder and that it would be advisable not to go any further. There are traps and powerful defenders. The rogue takes this as even more of an invitation to go down.
To be fair, "adventurers are hired for a mission, they stumble on an unrelated dungeon/quest, it nets them a thousand times more XP and gold than the mission" is a common enough plot.
Out of earshot of the orcs, the party berates the rogue for being a racist and a potential murderer.
Since the player clearly hadn't understood the whole "orcs are not monsters" thing, this should have been done out of character before he even attempted the ambush.
At the end of the round, with the alarm still sounding bursts out of the end of the hall, a gollem. A solo monster that is 4 levels higher than then they are. "Come on," says the rogue, "we can take him, the DM wouldn't put a monster in here that was above our level." [...]
They also took issue with me throwing a monster at them that was 4 levels higher than them but I figured since it was a completely optional encounter that they could have avoided or fled from, it was fair game.
Again, this is the point where a preemptive OOC explanation is required, if your campaign is indeed the sort in which the players might stumble on a dungeon too dangerous for their level. (Although if it was a MM1 golem, this dungeon was not one of them.)
The rogue is bound and gagged for the remainder of the journey.
I hope there were no hard feelings. From the point of view of the rogue's player, I'd be annoyed at the unfair punishment.
People I told the story to took issue with me having as sort of alignment test. You see orcs in a dungeon, most players are going to assume they are there to be killed. But I thought it would be fun to subvert the expectation. Had the players killed the orcs, their guide, who is himself an orc would have left them in disgust and told the humanoid tribes about them, giving them a penalty to their reputation, a system I made up.
Once again, if the whole group understood that orcs are not monsters in this world, this is fine (and they'd only have killed the orcs if they were roleplaying unscrupulous bandits). But if one or more player didn't, then you need to do an OOC explanation, not a metagamey "trap".
As for the people in this thread saying that metagaming should be punished in-game with grudge monsters/traps, well, I expect some of you will be immortalized in grognard.txt.