Joe Mixon was so confident he was gonna sign a big NFL contract before the 2017 Draft -- he dropped nearly $200,000 on some insane jewelry ... this according to a lawsuit obtained by TMZ Sports.
Remember, before the Bengals selected the RB with the 48th pick -- there were serious questions on whether a team would pull the trigger based on his violent 2014 incident with a female Oklahoma student.
But Mixon wasn't questioning himself ... and allegedly made at least 3 major purchases in February, March and early April which included the following items:
-- Custom diamond Rolex ($25,000)
-- Custom diamond necklace ($20,000)
-- Second Rolex watch ($16,000)
-- Men's gold and diamond tennis bracelet ($35,000)
-- Gold and diamond dog chain ($22,000)
Problem is ... when it came to pay the $190k bill, Mixon only ponied up around $100k, according to the jewelry broker, Eleow Hunt.
Hunt says he's been pestering Mixon for the $85k balance -- but he keeps getting crickets.
Of course, Mixon ended up signing a 4-year $5.45 million contract -- so, he's got the money.
We reached out to Mixon's rep who says he's unaware of the lawsuit.