Justin Bieber -- Selena Gomez is Not Lovesick ... She's a Drunk

Justin Bieber is scoffing at Selena Gomez, telling friends she has no one to blame but herself for her addictions ... TMZ has learned.

Sources with daily Bieber contact tell TMZ ... Bieber and his friends are laughing at Selena's "bad influence" claims, because they say she's always the drunk at the party. Bieber acknowledges he gets wasted, but whenever he had parties Selena was downright competitive ... smoking as much weed as the guys and sometimes outdoing them. They say she was also HEAVY into booze.

We're told Justin believes Selena's parents are behind the blame game, because they HATE him. He thinks they are fueling Selena's anger and making him a scapegoat.

Justin says he's happy he's no longer with Selena because she's just too high maintenance ... and out of control.