Mr. Wonderful ain't exactly shy when it comes to his opinion ... and the "Shark Tank" star just let Magic Johnson know why the NBA legend done MESSED UP by quitting the Lakers.
Kevin O'Leary wasn't disrespectful -- in fact, he likes Magic a lot -- but he thinks the guy made a huge mistake Tuesday night by suddenly stepping down as Pres. of Basketball Operations.
"He made a decision which I think was the wrong one," Kev told us on his way out of ABC Studios in NYC.