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 .