One of TV's most consistently irreverent and heartwarming shows gets sharper still in Scrubs: The Complete Second Season, as the Sacred Heart staff encounters more pratfalls, pricks, and personal strife. What other series boasts an a cappella version of the Charles in Charge theme, a character named Johnny the Tackling Alzheimer's Patient, and an object of affection known as T.C.W. (Tasty Coma Wife)? And the stunt casting of Heather Locklear, Rick Schroder, and David Copperfield (in a hilarious geek fantasy) is downright inspired. EXTRAS The making-of looks suspiciously like leftover footage from the season 1 DVD outing. But ''Imagination Gone Wild'' (fantasy sequences mapped out) and ''Secrets and Lies'' (on-set jokes revealed) are good, quirky fun. In the commentaries, we learn that Braff is obsessed with his hair, Ken Jenkins (cranky chief of staff Bob Kelso) doesn't understand half the one-liners he delivers, and there are economic advantages to filming a morgue scene (''You can get corpses for so cheap these days,'' Braff explains).