I used to crack my fingers, but then I decided to quit. I carved a line on my left arm with a rusty knife for every time I cracked a knuckle and I repeated this until I eventually stopped cracking. I lost a lot of blood in the beginning, but it was worth it.

(In reality the knife was a pen, the arm was a notebook and the blood was ink, but when I tell this story to my grandchildren in 40 years it'll definitely be rusty knife, arm and blood.)