Floyd Mayweather got into a shouting match with a heckler on the streets of NYC on Monday night -- after the fan accused Floyd of running from Gennady Golovkin.

Oh, and the video ends with Floyd's bodyguard threatening to choke a dude out.

Good stuff!!!

It all started after Floyd and his TMT squad left the Knicks game at MSG -- when a very loud fan started screaming at Floyd that he's scared of GGG.

Floyd yelled back to explain why he's not scared ... more yelling ensued. Floyd tried to jewelry shame the heckler -- asking how many diamonds he has on his watch.

As for GGG, he previously told us he wants to fight Floyd BAD -- and guaranteed he would knock Mayweather out cold.