Don’t. Even if you understand what you’re doing, someone else won’t and your family will die in a house fire.
Male-to-male end cables allow for the two leads of an open male end to make contact with anything conductive (including your flesh, causing some pretty gnarly burns) to complete the circuit and start a fire. No conscionable electrician will make these for you. It is the dumbest solution to any problem you’re looking to solve. Don’t.
Just a reminder coming up on Christmas.
I had to check if this really is what OP describes. Yes, it is:
Argh! Order a deathtrap from AliExpress!
(I got an electric shock from one of these once - hand made by my landlord - and tbf I’m still alive, but really, don’t)
What is the use case for this
Never mind I saw the other comment
Sometimes people put Christmas lights up in the wrong direction and try to use this as a quick fix rather than taking the lights down and reversing them.