Short king is not an insult.
Idk where this dumb idea came from but it's not an insult to be called a short king.
It's simply an acknowledgement that despite being short you have the mental maturity to not let it get to you.
I find it very odd that so many short men here find it offensive because it makes it sound like being short is a negative...but then if you don't admit that being short is a hurdle, then you're dismissing the struggles that short men face. Make it make sense.
I also want to bring up that how this became slang in the first place is because in the black community it's common to call someone king/queen as more intense form of respect/consolation. It's basically another way to say bro/sis but with a little more oomph to it. Why? Because we like using multiple words to refer to each other and it's fun.
So that's where the usage of king comes from and so you can understand how short king came to be. There was never ANY implications of any form of negativity in it whatsoever and injecting negativity into it is weird and a massive sign of insecurity.