Lindsay Lohan is firing back at a store owner who claims the actress stole a $2,500 necklace last month -- telling friends, "It's bulls**t ... I don't have any necklace."
Lohan also claims the person who filed the police report against her is "nuts" -- despite surveillance video that we're told shows Lindsay wearing the piece inside the shop.
As we previously reported ... the LAPD obtained a search warrant to sweep through Lindsay's house for the item -- but one of Lindsay's associates returned the necklace to cops before the search was executed.
So far, Lohan hasn't explained how the necklace got out of the store and into her associate's possession.