I will probably think of more, but these should be good for a start.

A member of the party had managed to make it into a section of the pixie stronghold where the women and children were located. One brave lady came before the party member with a dagger in her hands.
Pixie: You are one of those that have been raiding our village and eating us.
PC: What? You mean that you are good to eat?
DM: I am not going to bother with a Diplomacy check, as I am ruling that you just failed it.

================================

One of our younger players doing something younger players tend to do.
Young player: My character is going to Tumble in next to the monster, then Jump on its back.
DM: Make the check.
Of course the character makes it, as the young player put a lot of points into those two skills. Considering that he makes it on the back of the monster, he then manages to get on the monster's back. Now one of my power gamers speaks up.
Power-gamer: He should give us flanking.
DM: He does not give flanking.
The power-gamer picks up a ruler to show that a line passing between his character and the character upon the monster will pass through the monster. The DM is not fooled.
DM: You have to be directly opposed to give flanking, also, the character on the monster's back is not threatening.
Power-gamer: What? Why isn't he threatening?
DM: Because he is spending all his energy simply hanging on.
Power-gamer: Looking to the young player - What weapon do you have?
Young player: A short sword
DM: If he uses it, I am going to force Ride checks, and I don't believe that he has points in Riding this type of creature.
Young player: I didn't put any points in Ride.
Power gamer: Then what good did it serve gaining its back?
Young player: I thought it was cool.
DM: It was cool.
The power gamer puts his head in his hands.

Man. I really, just want to see this in action. Not that im against strategy in the "pwrgamer sense' but this is the best i think, it could have been handled.

You said; "hell..why not? let see where it goes...to the fella who said 'eh, im gonna go for it' you had fun, the newbie had fun, and the fella pretty much loading the dice said...'damn'. good show sir...i mean, in the end, you know what will be a lark, and what will, well...e a bit to overbearing. godspeed to your next post.

One time WAY back when our group was playing d&d, I was the DM. They were fighting evil treantlike monsters and somehow Kevin's character got turned into a tree, by another player's spell maybe. One of the treantlike monsters then showered him with pollen. Later Kevin said in-character "It's not my fault my first sexual experience was with a tree!" LOL! Later that campaign I had a half-tree/half-human girl show up that was his daugher. (just before the spell ended I said a nut fell off of Kevin's character - but they didn't put any significance to it).

Another time they donated some gold to a temple and the NPC priest said, and I quote, "Yay! We can afford booze and hookers again!"

Good times!

Ha Ha!

My husband tells a story from before I knew him (so this is a 20 year old gaming story!) about a time when a PC was turned into a tree and set on fire. He knew he was doomed, but was hoping to be resurrected, so he shouted to his fellow gamers, "Save a twig! Save a twig!"