A humorous way to say "penis". This term also refers to the fact that a fire extinguisher squirts water to put out fire, and so could someone's penis by urinating.
Someone: "What's that bulge on your pants?"
Funny guy: "It's my fire extinguisher!"
throws a cigarette on a dry ground
Someone: Hey, this could start a fire!
Funny guy: "Luckily, I brought my fire extinguisher with me" then whips out his penis and urinates on the cigarette.