My local hardware store has one of these signs. I managed a different hardware store about a decade and a half ago, and I also made a very similar one. (Mine was nicer, and routered out of a scrap piece of plywood.)

You would be amazed at the number of times we'd get asked that question. Typically it involved a story along the lines of, "Well, my wife started putting up her end of the Christmas lights at one side of the house, and I started putting up my end at the other side of the house, and we met in the middle, and..."

Westboro Baptists updating their signs

Plug first, check of the repairs are done correctly later, is what i always say.

The USB of power cables?

The two outlets could be on different circuits, if for example one of them is connected to a switch on a lighting circuit.

Then, the cable will be powering one circuit from the other. A circuit limited to 20A could draw 40A before blowing, causing damage to the wires.

Someone might do some wiring work on the lights, and shut off the lighting circuit, and still get zapped (though most electricians would test it before touching it, since breaker labels are rarely accurate).

There are many creative ways to die to a cable like this.

Most people would use it to solve Christmas light screw ups which means there would be another male and sticking out exposed later in the line. Just as dangerous there.

Extention cords are dangerous because they are not always the right gauge.

People get cheap extention cords and try to pull more power than the cord can handle and it ends up heating the cord and causing a fire.

It's why a lot of things say "Do not use an extention cord! Plug directly into wall." Because they know someone is going to use a dollar store extention cord on a space heater.

Not because the space heater won't work with an extention cord

Most people care about plug type (low profile) or color more than they do the quality or gauge of the wire.

Anyways, this cord could be dangerous like that if the gauge isn't the same or thicker than what's in the wall.

ah yes, a suicide cord. that's why there's warnings about them in every hardware store.

you can't stop stupid, but you can inform people they are stupid.

yes, it works in a pinch, but when you're cold and stressed when power goes out at 3am will you remember to plug it into the wall first? will you remember to cut off mains before you turn on your generator? will you remember to do the steps in reverse when power comes back?

I'm harsh because I've almost killed myself with one before, because I'm an idiot who (just like everyone else) thought, "I'm smarter than most people when it comes to this stuff".

get an interlock kit. save yourself and the lineman.

"bad things would happen" if we somehow enabled the mains to the power company.

There's a reason code requires generators to have an interlock with the mains, and it's primarily so people don't electrocute lineworkers.

Also be warned that you must plug in any generator as close to the breaker box as possible. Outlets and their wiring far away may be underdimensioned for powering anything significant further away. Also be warned that everything you're powering together must be limited by the dimensions of the one outlet you're using. The wires don't know any difference between AC in or AC out. For example it's max 10A? Then that's your limit for everything combined.

He went on to explain that most outlets have a safety mechanism for this scenario built-in.

wat? The only dangerous part of this scenario is when you only have one end plugged in and you have a hot, male plug. Unless you reverse one of the ends, the outlet wont react and if you do short it by reversing the ends, the Breaker, not the outlet will cut off the power.

Also, you also shouldn't have male-to-male cords in the first place.