From early on, I've used
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?