From early on, I've used こら and ほら somewhat interchangeably. They both mean "hey!"
I picked them up from friends early on without really having a sense of the difference.
Now, after some time, I've come to understand that ほら is simply "hey!", as in just getting someone's attention, and こら is "hey" with a flavour of "dude, what the hell?" mixed in.
The thing is, I still tend to slip and use こら when maybe I should say ほら, and vice versa. Old habits die hard.
My question is, when I mix up and say こら instead of ほら, how bad is it?