I was, (probably expired now,) a Firefighter instructor in the State of Michigan. Often a first day academy assignment was,
"Define and explain the terms, "Fire Plug," and Plug Ugly."
Back then there was no Internet, so the students were forced to go to a library and do actual research.
Usually we had some silly prize, such as a broken nozzle mounted on a nice plaque which was awarded to the first to bring us the correct answer.
"The first firefighters to put water on the fire were paid by the insurance companies. The competing local fire departments would often fight, coming to blows, over the privilege and the payout afterward. Engine crews, knowing that whoever controlled the water would extinguish the fire, would send the meanest, toughest, goons they had ahead of the pumper to guard the plug. Anyone from another crew who came near it would have to fight him. This is where the term plug ugly comes from."
Why wouldn't my paris pay for a 'net connection when I was a kid?