Starlets, you never learn, probably because you're not paying attention, probably because you're always as strung out as Twilight star Kristen Stewart looked last night on the Late Show: You must come on David Letterman's program caffeinated and at least attempt to say several interesting things. Mary-Kate Olsen's "so tired" complaint bombed; Lauren Conrad got entertainingly insulted for being otherwise boring. This is the price from promoting (usually vapid) movies from the Late Show couch. Stewart's appearance is one for the protocelebrity textbooks; an epic trainwreck progressing (in the clip after the jump) from severe awkwardness into mild nastiness and, at the very end, a devastating cut spun from precious, precious terrible awful comedy gold.