Let's see:
First, a couple of funny blunders from my all-time favourite DM (too bad he can't run any more games, and hardly ever play):
1. In this Campaign (our first 3e game, and I was the only guy who ever roleplayed before, though Baldur's Gate and the like was played before), we had a home base - a town with wizard college attached to it. We hear that it was about to be besieged by an army of undead, and headed there - we asked how long we would take to go back (no teleporting at that time). "2 and a half days if you hurry, otherwise 3 days." Thinking that it would be better to arrive well-rested, and not believing that they would get there that fast, we decide to take the 3 days.
We arrive with the city fully under siege - the DM expected us to hurry, so he had to adjust things. We fight a vampire (I think it was a cleric of velsharoon), got drained a bit and all that, and proceed to the war leaders. And during the travel, someone says: "He, isn't it noon?" "Yes" "And we just fought a vampire in broad daylight:" "Uh....."
See, we were supposed to arrive in the middle of the night. Noone, including the DM, noticed that because of our dawdling, we arrived 12 hours later, in the middle of the day, until 15 minutes real time after that fight.
2. Same campaign, much later. We were out partying in a tavern (well, gathering information and relaxing combined). The dire bear animal companion had to stay outside, and when the druid's player asked what the bear was up to, the DM replied: "Well, it will probably have eaten a couple of children that played on the streets." Which prompted our surprised answer: "Children play here at 2 o'clock in the night?"
This was probably to balance out the daywalker from before.
3. Same DM, D20 Modern Stargate Campaign. We were about to confront the BBEG in our last session, a former Guawossname who had enslaved one of those god slug thingies to harness its power. As we arrived at his base, he tells us that we can go again, he has no quarrel with us (usual BBEG banter). Well, we did - after we got his assurance that he won't bother earth in the next couple of centuries (which he agreed to, since he wanted to make war upon the System Lords, anyway).
Of course, the DM punished us for evading the final fight (which probably took hours or preparation) by saying that the guy failed enslaving the god-thing and later invaded earth, killing every one.
I guess he never figured that we would actually walk away from a big fight. And boy was he wrong.
4. Campaign after that. We're in the Zulkir of Evocation's very Citadel (or was it Conjuration? Well, one of those really powerful overlords of Thay, anyway). A trap was sprung upon us - the passage we snuck in by collapsed, teleportation was impossible in the whole structure, except in a couple of places - which were probably just past the Zulkir himself.
So I asked: "How much of that corridor was caved in?"
"At least 30 feet, no chance of digging through, it's a lot of stuff and you don't have the equipment."
"That's okay, I manifest disintegrate as often as it takes to clear the way."
"........ Damn! You did it again."
And so we did. Another final fight evaded. He tried to prevent it, but forgot about my psion and his power points enabling him to manifest powers dozens of times.
I have more, from other DMs, but they aren't nearly as funny (more the frustrating kind). If you want, I'll tell you about those another time.
