nakey bastard
a person who shows their butt or no clothes whenever they feel like it; they think you’re a loser for getting upset about it.
'My cousin is a nakey bastard. He walked into the kitchen in the middle of dinner with nothing on.'
'My mom called me a nakey bastard for wearing pajamas to the grocery store.'
'He's a nakey bastard. He came to my birthday party with no shirt and no pants.'