Citing some of his own antics, fellow American and seven-time grand-slam champion McEnroe also defended Williams' claim during the final three months ago that men have got away with far worse.
Williams was given a game penalty after calling umpire Carlos Ramos "a liar" and "a thief" in the second set of her straight-sets defeat to Naomi Osaka. During the tirade, Williams also suggested Ramos was sexist because he would have not have treated a male player so harshly.
The incident divided the tennis world, but speaking at the Royal Albert Hall where he is competing at the veterans' Champions Tennis event, McEnroe said criticism of Williams was wide of the mark.
"To who?" was McEnroe's dismissive response when asked if Williams should apologise for her rant that called Ramos's integrity into question and overshadowed Osaka's maiden grand-slam title win.
On the seriousness of accusing Ramos of sexism, McEnroe said: "She used a lot of cards. If thief is the worst word she used, I have got some bad news for you. There are a lot of other players, including myself, in a lot of other sports, that have done far worse. Not that it is the best thing to be called a thief but come on.
"If I use a four-letter word and say that you are a blanking, blank, which let's say hypothetically I have used in the past, do you think that would be worse than saying that you are a thief? To me it would be."
In McEnroe's eyes, Williams and Ramos were both to blame for the way the incident unfolded. He suggested that in such a big match, Ramos should not have been so officious in giving Williams the initial code violation warning for on-court coaching.
"She was wrong and so was the umpire," said McEnroe. "They are both wrong. We all know that people coach all the time, right? This guy suddenly decides to call her on it in the final of the US Open. Really? She was upset about it, and then she went after the guy later in the set and obviously was venting.
"And then he was letting it go, you have got to say to her, in my opinion, 'Look, if you keep going, that's enough. I'm not letting you go any further.' But you have got to give her the respect of a warning.
"I think he was wrong not to say: 'If you say anything else, it is a game penalty'. I am not even sure she knew it was a game penalty. That just threw the whole thing. He became part of the whole thing. I think it was badly handled by all concerned."
McEnroe then added with a smile: "Not that I have any experience in that."
Williams, who has said little on the incident, will have to address it at the Australian Open next month, but McEnroe believes she will not be unduly bothered. "I doubt that's her major concern right now," he said. "I think people would actually be behind her because she's still playing."
Should Williams win the title in Melbourne, she will draw level with Margaret Court's record of 24 singles grand-slam titles.