'Teen Mom' TOKES UP ... After Failing Weed Test

Four days after allegedly violating her probation by having THC in her system, "Teen Mom" Jenelle Evans gave off even MORE smoke signals -- sucking on what may or may not have been a pot-filled blunt.

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According to the North Carolina probation report, Jenelle tested positive for THC on July 13 -- the psychoactive ingredient in marijuana -- and even admitted to smoking out [also known as "smoking up" on the East Coast].  She was informed about the test results on July 15.

But on July 17, she posed for these pictures -- in which she appears to be smoking marijuana.

Jenelle -- who was put on probation after a drug-related conviction in April -- is due back in court in August to deal with the probation violation. Her lawyer had no comment.