It started with one ... just a lonesome Alfonso Ribeiro doing the "Carlton Dance" in L.A. ... when suddenly, hundreds of people rushed in and joined in on the Tom Jonesness ... and it was AWESOME.

It all went down at the Universal Studios City Walk in Hollywood -- where the former "Fresh Prince of Bel Air" star was leading a group that tried to break the record for the most people in North America flash mobbing at the same time. Similar groups performed at the exact same time all over the country.

Besides "It's Not Unusual" ... the gang also busted out the famous "Apache" dance that Carlton and Will performed during the famous male strip club episode.