I do it sometimes. Dunno why either, just when I'm really in the zone I feel like tapping my finger so I do.. LOL My brother used to do it when we played, so I think I just kinda picked it up from him?
I can say though that I've made a conscience decision to do it and not do it in the past. For some unknown reason I got into a really bad habbit when shooting on the money ball awhile back. Right before I'd pull the trigger I'd say to myself "I'm going to miss it" and even if it was a lock, my subconscience would find a way for me to miss it.
I can say in some instances I started tapping my finger as a way to take my brain off saying those words.. Kind of worked in a pinch to get me through the night until I could cure myself of that bad habbit.
DJ