Here is mine

Pathfinder game, we are a pretty large group composed of a ranger dwarf greedy as hell, an elven bard, a paladin gnome, a human priest, an half orc barbarian and myself an enchanter gnome.

I took the spell Light and the GM allowed me to light multiple target at once, the bard got the spell open door.

We come across a set of doors and we agreed the bard the GM and myself that if the dwarf decided to open a door it would lit up and smah on his face. The priest didn't know that and does a check to know what is going on, he then proceed to convince the dwarf that the set of doors is actually a lock to a hidden passage leading to a treasure. The dwarf then proceed to test every possible door combination as the GM keeps playing along giving random doors opening/closing/lighting up, as we are all laughing to tears. He finally understood what was going on after 30 min of uninterrupted laughter.

What's yours?