Laila Ali -- Sorry Mayweather ... My Dad's The Greatest!

Laila Ali has a message for Floyd Mayweather -- just because you THINK you're the "greatest," doesn't make it true!

Ali was leaving LAX yesterday when she told us she's not mad at Floyd for BELIEVING he's the best boxer of all time -- in fact, she respects his mentality -- but at the end of the day, he's just wrong.

There's more ... we also asked Laila if there's ANY chance she'll ever get into the ring for a mega-fight with UFC superstar Ronda Rousey.