Opinionated pet peeve: "just can't" where "can't just" is correct.
"You can't just do that": there are formalities or prerequisites that I believe you're skipping
"You just can't do that": it's wrong for you to do that, and it should be obvious why it's wrong
@freemo each is correct in its own circumstance. It just irritates me to see them used like they're interchangeable.