Cool is cheering for your own team. I don't want a shirt with "LA" on it, and I don't chant about the Yankees. "Here we go, Celtics, here we go!" is cooler than focusing on the enemy.
The "Beat LA" chant was a moment in history ... by the time is was used in a Boston-vs-Lakers context, it was already little weird, and now it's not really any cooler than Orlando's shirts.
Go Celtics!