John Mayer seriously shaded Taylor Swift on her birthday

Just when you thought the dust had settled between these two, John Mayer goes and does something douchy like this... 

It was Taylor Swift's Birthday yesterday, and her very-long-time-ago ex John Mayer thought it would be the peeeeeerfect opportunity to throw some shade around. 

He took to Twitter, and tweeted out the below (before very quickly deleted it, but thank god for screenshots).

Tay Tay and John dated for 4 months back in 2009/2010, and their "nasty breakup" inspired Taylor to write one of her hit songs "Dear John" which he was obvioulsy not happy about. 

Taylor's fans quickly ran to her side, telling John to go and "look in the mirror" as that would, "teach you the definition of lame."

John also posted about his hate for the month on Instagram.