Khloe Kardashian is fed up with the harassment from a woman claiming Tristan Thompson is her baby daddy, saying her attempted 15 minutes of fame are up ... and Khloe's threatening to sue the woman if she doesn't shut up.
Khloe's attorney, Lynda Goldman, fired off a cease-and-desist letter to Tristan's paternity accuser, Kimberly Alexander, Tuesday ... calling her out for recently admitting to faking DM's from Khloe.
The legal threat, obtained by TMZ, reads, "You put words in her mouth that she never said and that she wouldn’t say.