XXXTentacion's straight-laced look -- button down shirt, with his locks pulled up and off his face -- was NOT enough to sway the judge, but it made for one helluva mug shot.
TMZ obtained the pic XXX took when he was booked into Miami-Dade County Jail Friday morning. We broke the story ... the judge locked up the rapper Friday morning following a hearing in his domestic violence case.
XXX could be looking at seriously hard time after prosecutors added 7 new felony counts to his case. The 5'6" 19-year-old is being held without bail.