TV personality Bill Boggs, who used to swim competitively, was doing laps yesterday at the New York Athletic Club when he noticed “the guy next to me is like a shark . . . he’s pushing off the wall swimming the length of the pool under water, while kicking on his back. ‘Hmm,’ I think, ‘this guy’s good,’ ” Boggs says. “We hit the wall together at one point and I give it all I’ve got to stay with him, and after three strokes I look up and he’s already coming back.” The speed demon left the pool before Boggs finished, and when Boggs got out, the attendant told him, “You were trying to race Michael Phelps.”