In their defense, in my younger days, I was replacing a gas water heater. Had the Black & Decker Book of Home Repair (not actual title, bit something like it). Great book for someone who doesn't know shit about shit and doesn't have money to pay someone who does...
Anyway, gas line had one of those "nut on the bottom pipe connects to the top pipe" setups. Pretty sure that's the accepted terminology. Picture in book was bass-ackwards. I cranked on that thing,, hammered it, even torched it (turned gas off long before, but still made wife leave the house). Eventually, flipped pipe wrench around and tried the other way...came right off.
I'll hunt down the picture tomorrow...