Break up the Big Three? Maybe down in Miami, where the trio of so-called superstars have the collective toughness of your average 9-year-old girl. But not in Boston, where the Celtics are on the verge of a huge postseason upset, and Kevin Garnett looks like he is about to hand previously undefeated Father Time his first career loss. You don’t have to like Garnett. You don’t have to like the stream of R-rated language that comes from his mouth after every good play.