>>In the common law of libel, the claimant has the burden only of proving that the statement was made by the defendant, and that it was defamatory.<<
Maybe, maybe not. It is more ambiguous than that when you look at the actual law, especially state by state.
Of course, this was expressed as an opinion and there is no damage, so it is all rather moot.
Good luck in passing this off as merely an opinion => "I have no idea why the woman was crying and I am AMAZED the macho-man clearly drunk passenger wasn’t tossed off the plane."
As for 'no damage', you called him a drunk in a public forum. It's not up to you to determine whether there are damages or not. That would be for civil court.