I have a good one, I have been dming for about a year now, and one of my friends has an annoying tendency to roll his dice all the bloody time. When im talking, when im figuring stats out, whenever he has nothing to do. Classic case of ADD. So one day,h e was particularily getting on my nerves, and i had them speaking with a nimblewright, an intelligent construct, and he goes to speak to it. To speak, all you have to do is talk right, no DC required...so naturally he rolls to speak with the nimblewright.
Fenix(my friend): I'm going to talk to him(picks up his dice)
Me: Ok you approach the nimblewright("You don't need ur dice for this one")
Fenix:(Not listening to me, rolls a d20)"I speak with him"
(He get a 1, naturally)
Me: You approach the nimblewright and attempt to say hello, you bite your toungue so hard that you take 2d6 lethal damage, and mumble incoherintly. You then collapse from the pain in your mouth, and the nimble wright looks at you in disgust.