John Mayer has firmly denied allegations suggesting he was slyly criticising his ex Taylor Swift after branding her birthday on Tuesday (13Dec16) the "lamest day of the year".

As the pop superstar marked her 27th birthday, the Daughters rocker took to Twitter and appeared to take aim at the singer in a cryptic message.

"Tuesday, December 13 may be the lamest day of the year, conceptually," he wrote.

Taylor's fans were quick to jump on the post and lashed out at him online over the perceived dig, but John refused to take the attack lying down and fired back at the Twitter trolls, insisting he was too old for childish swipes online.

"NOPE. No. Nuh-uh," he declared. "People I am 39. I am deleting those tweets. Come right at me for doing so. Absolutely no shade."

He did as promised, but followers had already taken a screenshot, which quickly hit headlines for all the wrong reasons.

John soon regretted removing the post because it only made social media users criticise him further, suggesting deleting the message was a sign of his guilt.

Returning to Twitter early on Wednesday (14Dec16), he added, "Looks like I shouldn't have deleted this tweet..."

John, who is over a decade older than the Bad Blood singer, dated Taylor from November, 2009 to February, 2010, and their break-up inspired the pop star's song, Dear John, in which she accused him of playing her with "dark twisted games".

He later admitted the track, which appeared on Taylor's album Speak Now, made him "feel terrible" and "humiliated".

"Because I didn't deserve it," he told Rolling Stone magazine in 2012. "I'm pretty good at taking accountability now, and I never did anything to deserve that. It was a really lousy thing for her to do."