a signature habit
inveterate - habitual
The word ‘inveterate’ was once used to refer to a chronic disease but has since been adapted to most commonly describe somebody who does something damaging or immoral very often and cannot stop themselves. For that reason, it also implies an addiction of some kind, making it frequently associated with vices such as gambling, alcohol, and drugs. However, it can also be used in a more neutral or positive sense, though that is less frequent.
Don’t listen to a word that salesperson says. The man is an inveterate liar.
There’s no point giving her any financial support. She’s an inveterate gambler and drinker, so she would just spend the money on feeding her addictions.
Emily is an inveterate reader, so she decided to set up a book club for people in her village.