Jin has put a lot of practice into controlling her emotions, especially her anger, but there are certain things that are guaranteed to royally piss her off. Chief among those being any kind of threat, verbal or physical to her loved ones. And the source of that threat will quickly learn just how good she is at channeling that anger into her fists.
And both Mary and Celeste are similar in that they will do their best to be courteous and friendly, but if pushed too far you'd best be prepared for one hell of a verbal beating (or physical in extreme cases)