... especially with all the crap Conor has been talking about Floyd lately!

Remember, it was just back in May that Conor told Mike Tyson, "I will beat Floyd. I promise my life on it."

Tyson had been praising McGregor as a "bad motherf**ker" for going 10 rounds with Floyd in their 2017 fight -- and McGregor responded on social media.

"Thank you Mike, and just know that for the inevitable rematch, with the knowledge I now hold of Floyd’s style, plus under the tutelage of my old school boxing coach, I will crack the puzzle, and I will beat Floyd. I promise my life on it."

So, when Conor unexpectedly announced his retirement from combat sports on Saturday evening ... Floyd was stunned and ready to talk some trash of his own,

“If I’m not mistaken, didn’t you tell Mike Tyson you could beat me if we fought a second time?" Floyd said.

"Now you're quitting! I thought you wanted to beat the best? Well, if you decide to come back, I will be waiting to punish you again."

Just a few months ago, Mayweather told us he was game for a rematch with Conor ... if the price is right.

No one really believes Conor is done fighting -- despite claims that he's bored with the fight game.

Most experts and insiders believe it's just another negotiating tactic to try and get a better deal with the UFC.

Will Conor reconsider for another 9-figure payday with Floyd? They ain't getting any younger!!!

Stay tuned ...