BOSTON — There’s an alter ego that emerges from Boston Bruins goaltender Tim Thomas when provoked.

We’ve seen it occasionally when he’s taken a swipe or a shove at an opponent he thinks is taking too many liberties while driving to the Boston net. Leave it to New York Rangers überpest Sean Avery to cause Thomas to unleash that second personality — let’s call him “Tank” — 10 fold and bring on a reaction like none we’ve ever seen before.

Take a look:

Thomas, mild-mannered 90 percent of the time, explained his decision to go after Avery after the Bruins’ 1-0 at TD Banknorth Garden.

“It’s an unwritten rule that basically nothing happens during a TV timeout, you know what I mean?” said Thomas, who now has five shutouts on the season. “I’m stretching there and Avery comes by,  and I get hit in the head with a stick. You look up, you see who it is and you’re like, ‘You’ve got to be kidding me.’ So it was just reflex.

“I mean, the battling during the game and stuff, I have no problem with that. I actually like the way he plays around the net; he’s tenacious, he gets in right around the crease, but he’s not actually doing anything illegal. I have no problem with that, but there’s lines that you can cross, and he seems to have a hard time figuring out what those lines are.”

With Thomas bolting for payback on Avery (who declined comment) in the neutral zone, of course Rangers goaltender Henrik Lundqvist had to leave his crease as well. Both Lundqvist and Thomas bonded at the All-Star Game back in February, so it might’ve been awkward for the two casual acquaintances to come to blows.

“He looks like a pretty strong guy,” said Lundqvist. “When he goes after one of our guys I have to do my job. I looked at the bench and wanted to get the OK to go over but it is a very important time. You don’t want to take any chances with suspensions or whatever you can get.

“I think he overreacted.”

Whether Thomas acted properly or not, he settled right back in and finished off the shutout.

“I want to be clear here in my assessment,” said head coach Claude Julien. “I prefer he doesn’t go in and do those things. He’s emotional, and he goes and does it. I prefer his teammates come in and protect him instead, but he did what he had to do.  He went back in nets and started focusing again and played a solid game for the rest of the game.”

There’s a strong chance the Bruins and Rangers will tangle again in the playoffs. If they do, they now know firsthand they’ll have to be ready for more Avery antics.

“You know he’s going to do something in a game,” said Julien. “He always does; that’s what he thrives on. So for me, it’s just you’ve got to keep an eye on this guy all  the time, even after whistles … he’s an expert at that, and that’s what he tries to do.”