Floyd Mayweather keeps racking up the accolades, this time getting his very own day in a major American city ... that doesn't seem to have anything to do with Floyd.

It went down back on January 17 when Floyd was honored in Oklahoma City, where the brass in town officially declared the date Floyd Mayweather Day.

There were festivities aplenty ... including a dinner, followed by a meet-and-greet hosted by industry mover and shaker Karen Civil.

This was no joke people, Floyd received official documents from the state -- making the whole thing as official as a referee with a whistle.

All of this is great, but what we can't figure out is WHY OKLAHOMA CITY!!??? We couldn't find any connection between Money and OKC ... and it's got us pretty bewildered.

This has gotta hurt Kevin Durant a little ... just a little.