In a campaign that ran for many years in the 80's, the GM had created a minor crocodile god called something like "Rezalezabgib" (something he stole from a Muppet Show episode, we found out later).
He first appeared when someone had stolen his eyes. Our job was to get them back. Whenever someone would say his name, he would appear, look for his eyes, and then eat them if one wasn't there.
Eventually we got the eyes back, but one was stolen again later. The GM was discussing something in character and forgot this bit. He, absentmindedly, had the character say "Rezalezabgib" and every single player went diving for cover - under the table, out of the room, you name it.