Charlie Sheen is BLASTING John Mayer for claiming he was defrauded by someone who sold him counterfeit Rolexes ... saying Mayer made a fortune off the watches and now just has a bad case of buyer's remorse.
TMZ broke the story ... Mayer is suing Bob Maron, a leading watch dealer, who sold the singer $5 million worth of watches ... and Mayer claims some had counterfeit parts.
Sheen says Mayer is hiding something -- that he re-sold a number of the watches for a HUGE profit. Charlie -- also a big-time watch collector -- tells TMZ, "WAIT!! Mayer spent $5M with Maron and is crying about $600K?!? Ask him how he did on the $4.4M...! Sorry that 7 of your 100 watches aren't to your liking! boohoo!! "
TMZ also reported Mayer posted on a Rolex message board back in 2007 that he was specifically looking for Rolexes with counterfeit parts, and Maron's lawyer says this is PROOF the singer is lying through his teeth when he claims he didn't know what he was buying.
Charlie adds, "Maron wrote the book -- period the end. Nothing but respect for Bob -- his integrity is beyond reproach! This calamity of buyer's remorse 7 years after the fact is clearly a reflection on John Mayer's character and not on Bob Maron's."