I know it seems obvious, but buy some nail-clippers lol ...no, really... I used to bite my nails a lot when I was younger and, after something caught my nail... tearing into the flesh, I made a concerted effort to keep those buggers trimmed. I rarely have troubles like that now lol
Procrastination, particularly when writing papers for school. Thank Heaven that is one form of procrastination that will be automatically cured next year.
My most annoying habit is seeing every choice I need to make as black or white, binary one or zero, I am sure there is a fancy medical term for this.