What a laugh riot for Hollywood insiders. On his first show back after the strike hiatus, David Letterman tonight introduced Jim Jackoway, the entertainment lawyer who helped negotiate the Worldwide Pants interim agreement with the WGA. Only it wasn't the real Jim Jackoway (photo left) of the firm Jackoway Tyerman Wertheimer Austen Mandelbaum & Morris. It was a goofy-looking teenager who crept out to the microphone and then ran backstage filled with fright.