Use 'propensity' to discuss a person's usual behavior, especially something done often. She has a propensity for arriving early.
Pro Tip 2/3
Neutral Tone
'Propensity' is neutral—neither formal nor informal—and fits well in diverse situations. There's a propensity to use smartphones compulsively these days.
Pro Tip 3/3
Not Always Negative
While often used for negative habits, 'propensity' can also refer to positive tendencies. He has a propensity to help others without expecting anything in return.