The UFC star took to Wrigley Field in Chicago ahead of the Cubs' match against the Minnesota Twins on Tuesday (21 September), but his baseball skills left a lot to be desired.
The Notorious was invited to throw the first ceremonial pitch of the MLB game, and the 33-year-old's wild attempt went miles too high and wide, completely missing the target.
Now, you wouldn't expect him to be an expert pitcher, but his truly awful effort left commentators and fans in hysterics.
However, the fighter seemingly doesn't see the funny side.
On Instagram, he has staunchly defended his pitch, arguing it was much better than 50 Cent's (37p's).
He wrote: "The audacity to compare mine with this p**s! Picture to picture alone buries this.
"Mine, bar the accuracy, was the most powerful and fastest first pitch of any of these other athletes/artists over the years. No comparison.
"Smoke them up and down that Forbes I do. Get Messi over. Smoked. Cris. Smoked. Federer. Doubled. All time Most Power! Put me in the Wrigley hall of fame for that rocket launch."
Presumably, McGregor is being a little tongue-in-cheek here, as his pitch was clearly totally awful, but given the ego of the man, it's hard to know for sure.
Indeed, there was plenty more of this ego on show in his defiant post.
He continued: "Anyway back to the pitch. Venom. Composure. Balance!
"The gold bar of Patek [his watch] almost came flying off me it was that fast and powerful.
"I'd take it back to @patekphilippe for adjusting but this watch is now discontinued. A rare. I Bought for 80k in Weirs jeweller of Ireland and today it is worth close to 500k. And going up.
"Fifty has a nice Hublot too. Big Bang. Small bucks 50cent. One has power. One is the director of media relations for some show called power.
"You know what it is. The Mac in Chicago!"
McGregor can say what he likes though, the people saw what the people saw - and they reckon it is right up there with the worst ever pitches.
Writing on Twitter, one user said: "Conor McGregor nearly taking out a fan with this pitch."
Echoing the sentiment, another chimed in: "50 cent has arguably the worst first pitch in MLB history.
"Conor McGregor: 'Hold my beer'."
"This Conor McGregor first pitch might be the worst one ever LOL," put a third.
While another added: "Folks I'm calling this as the worst first pitch in history. It's so much worse than 50 cent, Chris Rock, or Baba Booey because he's a professional athlete."
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