What a fun subject.
I always pick at pimples. Especially if they're bothersome. Relieving the pressure helps a lot for me, although it's a bit painful and gross.
I usually leave scabs alone, because I actually want them to heal. But sometimes it's too hard to resist playing with them, especially after a couple days .... but why?
Blissters, on the other hand, I leave as well alone as I can, because I'm terrified of getting an infection in one. If I do happen to puncture one, I peel away most of the skin (ick) and apply ointment and bandage it for a few days. Last thing I need is a little pocket to trap dirt and disease.
I also pick away at the excess skin around my fingernails. There seems to be an endless supply of it.
Jam it back in, in the dark.