Stupidity must be one of the Hilton family genes -- Paris' 18-year-old brother Barron has followed in his famous sister's footsteps by getting a DUI yesterday morning.

Sources tells TMZ that Barron, who lives at home with his 'rents, snuck out on Monday night and didn't come home. He was arrested at 8:30 AM yesterday morning after driving the wrong way on the Pacific Coast Highway and being followed to a gas station by a witness, who called the police and took Barron's keys. Barron's blood alcohol content was .14, which is nearly twice the legal limit for drivers over 21, but for anyone under 21, any BAC is considered legally drunk.

And get this -- Paris refused to bail him out of jail! "You're going to learn your lesson," she allegedly told him. Paris was "very upset and very disappointed in him." Barron's friends came to the rescue and footed the money to spring him from the clink around 6 PM yesterday.

If convicted, Barron faces a one-year minimum license suspension and could go to jail, but most first-time offenders usually get probation.