doing naughty things, being bad, doing something that society sees as bad or wrong, being evil, not caring, comiting a sin.
person 1: Hey did u comit a sin last night?
person 2: Yes, i had a one night stand, if that's what you ment.
I didn't listen to my parents. Oh, i'm so sinful.
I like that hot ass guy with tattoos! He looks so sinful.