Yo.
I don't know if you're aware but what you're doing has a name; dermatillomania.
I also do this although I also do it when I'm bored as well as stressed, worried, etc. It drives my other half insane & he's taken to tickling me if he catches me doing it (I hate being tickled so it works as a distraction & some kinder adversion therapy) I completely understand what you're saying about wanting to do it more when someone tells you to stop. Again, I'm the same, hence the tickling because if he tells me to stop my brain automatically thinks "**** you. I'm gonna do it more".
Maybe if you're not ok with having a full blown conversation with him you can simply ask him to hug you if he sees you doing it as this will help to reassure you and make you feel better.
I recommend getting something to keep your hands busy that you can keep in your bag. Tangle beads are quite good.
http://www.tangletoys.com/
If you don't have the money to buy one then pop to your local pharmacy and pick up an NHS quit kit for free as they stick one in there.