Mischa Barton is reportedly coming off of a recent stay at an Arizona rehab center … & according to paparazzi following the ex-OC actress, she hasn’t seemed to be able to stay sober for long.  Looks like art has imitated life from the small screen to Miss Barton’s real life.

Barton & a friend stopped by a low-income housing facility in Venice, CA earlier this week to supposedly buy marijuana.  When they returned to their car, they were observed sparking up a joint.

“Mischa appeared to be really enjoying the pot, taking long drags off of the joint before passing it to her buddy,” an onlooker tells.

After they got high, the group drove off to West Hollywood to take care of some last minute holiday shopping.

Let’s just hope Mischa remembered everyone on her list!

PS - WTF is up with her outfit???  That must be some good stuff she’s on …