Thursday marked two-time NBA champion Ray Allen’s 42nd birthday, and while we imagine the retired marksman spent a chunk of it playing golf in some exotic location, we know for sure the future Hall of Famer spent some of it arguing with Boston Celtics fans on Instagram. Which is quite sad, really.

We got here because Allen’s ex-teammates have publicly harped on his 2012 decision to join the Miami Heat for the past five years, and their outspoken contempt for him has only increased as they all enter retirement. Some Boston fans have taken that animosity to another level, so when the Instagram account “@bostonceltics4ever” posted happy birthday wishes to Allen on Thursday, a whole lot of fans responded by calling him a “traitor,” “snake,” “Judas Shuttlesworth” and much worse.

To which Allen responded with comments uncovered by internet sleuths on Twitter and Reddit NBA:

Allen also circled back to thank the fans who actually did wish him a happy birthday, which is nice, but the fact that Allen still felt compelled to address Celtics fans about this on Instagram three years after he last played a game in the NBA only emphasizes how bad things have gotten between them.

In the past few months alone, members of the 2008 Celtics opted not to invite Allen on a vacation celebrating the forthcoming 10th anniversary of their championship together, and Kevin Garnett hosted an “Area 21” segment for TNT during the playoffs in which Paul Pierce, Rajon Rondo, Kendrick Perkins and Glen “Big Baby” Davis all explained on national TV their rationale for disliking Allen.

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Afterwards, this photo of Allen playing for the Heat against the Celtics was posted to his Facebook page with the caption, “The power to push limits,” before being deleted and labeled as another hack:

In interviews over the years, his ex-teammates didn’t quite go as far as some of the folks on Instagram, but Kevin Garnett called Allen disloyal, Rajon Rondo dubbed him the “enemy” and Paul Pierce described the ordeal as a “betrayal.” And while they have publicly spoken about him, it seems they have privately not spoken to him, which for a team that embraced “Ubuntu” is a bit depressing.

All of the animus is focused on Allen’s decision to turn down a two-year, $12 million offer from the Celtics, including a no-trade clause, to join the Heat for three years and $9.5 million shortly after the two teams met in the seven-game 2012 Eastern Conference finals series. Even Boston coach Doc Rivers told Yahoo Sports at the time, “I was pissed at him. I was pissed at him for his reasons for leaving.”

It was not a cordial breakup, but after repeatedly being dangled in trade talks — including one that would have sent him to the Memphis Grizzlies for O.J. Mayo that came awfully close to happening — and losing his starting job to Avery Bradley during the 2011-12 season, Allen was ready to move on. Rumors have lingered about Allen’s on-court chemistry with Rondo and his off-court relationship with teammates playing a significant role in that decision, but for whatever reason, he felt the desire to chase one more ring elsewhere, taking less money and playing a valuable role to accomplish that goal.

These are all points that have been made over and over again — and reinforced by Allen on Thursday.

Pierce has suggested it was a lack of a phone call about Allen’s decision that hurt most, but he’s also the one who believes a mending of their relationship could be coming. Although, Garnett continues to imply that while they are the true Celtics, Allen is not, because he left when they still felt like they had championship hopes. Of course, Rondo tore his ACL in 2013, those Celtics never really had another title shot, and Boston’s recent trade of Bradley marked the last vestige of the “grit and balls” Celtics.

Perkins was traded to the Oklahoma City Thunder, Davis got signed-and-traded to the Orlando Magic, Garnett and Pierce were dealt to the Brooklyn Nets, and Rivers orchestrated his way to the Los Angeles Clippers. In the years since, the Celtics rebuilt the roster to reach the conference finals for the first time since 2012, and the organization just gave Allen’s No. 20 to incoming All-Star wing Gordon Hayward, indicating that number will not join Pierce’s 34 and Garnett’s 5 in the TD Garden rafters.

You might think that would close the book on this strange chapter, but a couple Instagram comments from Allen on his birthday kept the pages turning, which seems about right for this paperback romance. Really, though, the only bombshell in this latest edition was Allen writing, “I will always be a Celtic no matter what any of you say,” which seems to suggest the hostility only flows one way.

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Ben Rohrbach is a contributor for Ball Don’t Lie and Shutdown Corner on Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach