i think the uncivil atmosphere you speak of has coincided with one of the most frustrating seasons in Celtics history, for some very specific reasons:
1) the Celtics are the proudest franchise in the league. we have had to endure a 20-year title drought that was brought on by one unbelievably tortuous twist of fate after another. adding insult to injury, us Celtic fans have had to endure watching the Bulls, Spurs and Lakers win multiple titles in our absence.
2) the arrival of Kevin Garnett and the immediate effect that he had on the team was like a warm balm that brought healing to our collective wounds. the team magically became the Celtics again, caring about winning above all else, playing the fiercest team defense seen by the NBA in many years and most of all, playing together as a team, beautifully. the championship that followed was like a miracle. only one year previous, banner #17 seemed as far away as it ever had, and now, the championship trophy was back where it had always belonged - in Boston.
3) the frustration and pain that would follow the euphoria and satisfaction of the championship started with the summer-long holdout and subsequent loss of james posey. we still haven't replaced the guy. still, the Celts started the next season fast - very fast. but the christmas day loss in LA was soon followed by the injury to Garnett that ultimately derailed the title defense. the loss of Leon Powe - another beloved member of the title team was followed the next season by the trade of Eddie House.
4) then came the amazing playoff run that saw the Celts simply dismantle the two best records from the regular season. winning at cleveland and orlando almost looked easy. then, of course, came the hated Lakers, the amazing wins in games 4 & 5 at home, followed by game 6 & Perk blowing out his knee after getting hammered off the top rope by Bynum. then, of course, came game 7, which for me, a Celtics fan of 40+ years, is now the most painful loss in our history
5) this season felt like a re-birth of the 2008 championship group, but with the addition of a togetherness forged out of everything they had been thru - four seasons together, the title, the loss to orlando, the injuries, and most of all, the unity that resulted from the aforementioned game 7 in last year's finals. the team was playing their lights-out defense again, KG looked like his old self, Ray Ray and Paul were playing great and Rondo was knocking the top out of every assist record he could find. most of all, the Celts had a shared motivation that you rarely see in professional sports. they didn't just want to win the title this year, they NEEDED to.
6) and then the trade that took it all away. the playoffs were going to be our revenge and redemption. this team had become a special group for so many of us. they cared about each other in a way not usually seen in pro sports. i mantain to this day that the Celtics simply have not been the same team since Perk left. watching them struggle the last two months of the season, seeing them get bullied by other teams they use to bully, like Chicago and Miami. they have lost their identity and their confidence. no amount of "playing hard" can bring that back.
and that Roy, in brief, is why i think you are seeing the extreme anger and confrontation that you spoke about above, within the Celtic family. at this point, it's just a little too much to take and the thought of the Lakers pulling even with us or the Bulls or OKC (with Perk), or God Forbid the Heat, starting a run of titles is just more pain than i can handle.