Unquestionably, it is a bad habit.* If it's very bad, I suppose that's what we call an addiction (like bulemia, ...etc).

Anyways, assuming you have this bad habit, like I did, since childhood.

The best thing I ever found to change this habit is to 'interrupt' myself everytime I feel like the old habit is creeping back in.* I interrupt myself by (quite literally) asking myself, "WHAT DO YOU REALLY WANT".* Since I know that I want to be healthy & thin, this process helped me to get rid of my old bad habit and install a new (healthy) one.