Play video content EXCLUSIVE 1/13/17 TMZSports.com

Floyd Mayweather is shooting down Dana White's $25 MILLION offer to fight Conor McGregor ... saying simply, "You're a f**king comedian!"

Earlier Friday, White appeared on 'The Herd' on FS1 and made the official offer for the fight -- $25 mil each plus part of the Pay-Per-View profits.

Floyd was clearly INSULTED by the offer and told us to look at his watch ... a limited edition Hublot Laferrari which usually starts around $220k and can run up to around $350k.

The message ... Dana's number is WAYYYY too low.

Back to the drawing board.