Pertaining to a novacaine fetish when you stick your thumb in a jar of novacaine and let it go numb. You then suck on your thumb until you regain feeling.
"What are you doing after work?" walrus asked
"Why I'm going to give myself the numb thumb." peter pan replied
A soreness or pain that you feel in your thumb after playing video games for too long. Originated from the Nintendo NES controllers because the movement pad had sharp edges on it and extended play would jab those edges into your thumb making it sore.
"Dude, I've been playing for hours and man does my thumb hurt. I think this controller gave me numb thumb..."