(from a game of D20 Modern I once played)
DM: I wouldn't pee on that fence...
PC: Why not? It's just a fence.
DM: I wouldn't pee on that fence...
PC: *eyeroll* I unzip my pants and pee on the fence.
DM: ZzzzZZZZzzzzt. 220d4 electricity damage.
PC: WHAT??
DM: Told ya not to pee on the fence. It's an electric fence.