This one happened a while back. One of the other members of my and Mr. GR's gaming groups was DMing this one (it was his own campaign, not a jointly DMed one). Party consists of a drow paladin (me, using a variant I found online that was well balanced and didn't have quite as strict a code. I normally don't play paladins, but I was doing an example paladin to show player #3 how to RP one, since he always seemed to play them as smite happy maniacs) a Deep Imaskari wizard (Mr. GR), and a half-drow monk. This was a mostly Underdark campaign in the Forgotten Realms, and no, I was
not playing a Drizzt clone. At this point, we'd come to Waterdeep after some stuff in Skullport. Now this problem stems from the fact that player #3 has occasional problems remembering certain aspects of his character (read: race). That and he had insanely bad luck.
DM: Alright, you come up amongst some shacks in the slums.
Me: I put up my hood, and put on some gloves.
DM: There are some kids playing around outside. There’s also a guy leaning unconscious against a shack wall, obviously starving to death.
Me: I'm gonna walk over, drop a few gold on the starving guy, and walk off towards a slightly wealthier part of the city.
Player #3: I'm gonna' walk over and watch the kids.
DM: They take one look at you, and run away screaming.
P3: Huh?
Mr. GR: Dude, you're half-drow, so you look like a full drow! Get out of there before they tell someone.
P3: Should I knock them out?
Everyone else: NO!
P3: Oh yeah, I'm lawful good, right.
Some time later and after a bit of other junk.
DM: You arrive outside of a tavern.
Me (after having used a disguise kit to make myself look like a surface elf): I walk in and order a drink.
Mr. GR: Same here.
P3: Same here.
DM: Oh god, here we go again. You look a frigging drow!
P3: But I’m wearing a hood!
DM: Yeah, and remember you’re also wearing a short sleeved monk shirt. They can see your
arms! They all start pointing and screaming!
P3: Alright, I’m jumping out the window.
DM: OK, but remember that there are people outside.
P3: I run around to the other side.
DM: People are streaming out of the door on this side, but there are still a few escape routes.
What you gonna do?
P3: I’m gonna jump through that window there!
DM: If you would please look at the map, you just jumped back through into the tavern again.
P3: Crap! I’m jumping back out and running!
He manages to get away from the mob, but is running through the streets. The other two characters have been trailing after him.
DM: Alright, they are still after you. There is a brick building here, with a large sign in fro with the Waterdeep crest on it. There are also plenty of buildings around. The street is empty.
P3: I'm running into the brick building.
DM:

Why?
P3: To shake off pursuit!
DM: You just walked into a guard garrison. There are soldiers sitting all around.
P3: Uhoh...
Me (walking in): Where are the prison towers, I'm supposed to deliver this prisoner to them.
DM: They give you directions to the prison towers.
Me: I grab him and drag him out the doors.
We get just a little way down the street when...
P3: You know what? Skip that, I'm no one's prisoner. I'm marching back in there, and they either accept me or the don't.
DM: What!?
P3: I march back in there. I walk up to the closest guard and start singing "Why can't we be friends."
Me and Mr. GR: Oh god...
Be aware that alot of other stuff happened that day, to this same PC (this was all in one meeting), including Mr. GR having to pull him out of an indoor market where the monk had ende up knocking everyone out to make sure no one told the guards.
We still poke fun at him about it.