Jenelle Evans: Arrested For Failing Drug Test After Plea Deal, All Smiles in Mug Shot!

Jenelle Evans' latest mug shot is here, after she failed a drug test after her latest court hearing ... in which she struck a plea deal to keep her out of jail.

At least she was in good spirits, apparently:

Jenelle Evans: Arrested For Failing Drug Test After Plea Deal, All Smiles in Mug Shot!
The Teen Mom 2 star was in court earlier, answering to charges of drug paraphernalia, heroin and Percocet possession, stemming from her arrest in April.

Jenelle Evans agreed to a plea bargain in which she pleaded guilty paraphernalia charge, in exchange for the other, more serious charges being dropped.

She was hit with 18 months' probation, but no jail time - amazing, given that she was busted with major quantities of the drugs and assault on her husband.

That charge was dropped when Courtland Rogers pleaded guilty, so all was looking up for Jenelle ... until she was randomly drug tested and failed.

Later this morning.

The MTV star tested positive for marijuana and the judge sent her to jail for 48 hours, her (hard-working) attorney Dustin Sullivan confirmed to TMZ.

It's unclear why she was in such a good mood at the time officers booked and processed her at the station, but ... better than being suicidal, we guess?

It's also unclear what impact it will have on the probation terms she just agreed to and when, but you can guarantee there will be consequences.

And that she'll likely be back in front of the booking photo camera before long, as she hasn't learned much of a lesson from her previous 245 arrests.