I love this one :
Player: But I'm at point-blank range, so I get a +4 modifier - so that means I hit.
Gamemaster: +4 modifier, huh? Citizen, where did you obtain this information?
Player: Huh? It's in the rules.
Gamemaster: Citizen. The rules are security clearance Ultraviolet. You are security clearance Red. For a citizen of security clearance Red to know data that is cleared only for Ultraviolets is treason
Other Players: ZAPZAPZAPZAPZAPKAPOW