My wife was stringing up lights on the garage wreath and had one strand turned around and wanted me to make one of these to “fix” it so it could plug in. It took a second to explain to her the other end was just going to be an exposed line voltage plug.

I'm sure Freud would have something to say about that "mistake".

I just recently did the same with a set of patio lights. Was shortening a set of lights which hang over my porch. Measured out the length I needed, cut the cord, attached a new female end. Went to plug the other end in… also female!

You’ll learn volts jolt but milliamps will kill you

The whole volts safe amps kill thing is so stupid though, you can't have any serious amps without serious volts, unless you have near-zero resistance, which a human body does not.

That's not always true. If the two outlets are on the same electrical phase, you may be okay. If they are on different phases, it would be dangerous.

People usually want them so they can run Christmas lights the wrong way, either because theyve already strung them up backwards or they're too dumb to figure out a better solution, but the end result if one end is left unplugged is an enormous amount of power just running loose at the exposed end. Even if you just wanted to plug it into the same outlet as a joke, if you plugged one end and touched the prongs on the other end while in the process of plugging the other side in, you're pretty fucked.

It will either instantly trip the breaker or do absolutely nothing, depending on how it's wired internally.

The real danger comes from when only one end is plugged in, though. With only one end plugged in, the other end becomes a 120V cattle prod.

They're illegal and it's only safe IF the home owner remembers to turn off Mains.