Lindsay Lohan is adamant ... she did NOT punch that fortune teller at a NYC nightclub this week -- but she did call her the g-word ... because the fortune teller's buddies tried to steal Lindsay's purse.

Lindsay's telling friends ... Tiffany Mitchell approached her inside the club Avenue early Thursday morning to do a reading, but Lindsay turned her down -- then noticed Tiffany's friends crowding around her purse at a nearby table.

When Lindsay returned to her table, the people in Lindsay's group informed her that Tiffany's friends had swiped the purse -- a super expensive black leather Celine -- so Lindsay angrily confronted the fortune teller.

Lindsay has admitted calling Tiffany a "gypsy" but says she did not know the word is considered a slur.

As for hitting Tiffany -- Lindsay's totally denying that ... and feels she's the victim of yet another setup.