Verified answer

It depends on the context:

Most of the time it probably means. "That thing that you've just done: I want you to be aware that I don't like it; don't keep doing that."

The only deviation could be if you're a seamstress making habits for a nunnery and a formidably promiscuous nun comes to you to get a cute décolletage cocktail dress made on the sly; She might say "Oi, Siobhan! Don't make it a habit, make it a sluty ballgown; I'm hitting the streets. Here's fifty bucks".

But it's probably the first one.

Don't keep doing it!!

It usually means you did something they didn't approve of and not to do it again.