I love when actors who are obviously smart (or so it seems to me) are such good actors that they can convincingly play dumb.  It has to be as hard as playing drunk, for the same reason:  you have to convey unawareness, and acting is nothing if not hyperawareness.  (Similar paradox to funniness - the way TRYING to be funny subverts itself.)  Reese Witherspoon's Elle Woods is an outstanding epitomic example.  And George Clooney's O BROTHER, WHERE ART THOU? character being a sample failure of same.  Anyway, thinking about this because lurve Paul Rudd's Bobby Newport so much... I actually believe that Bobby is a sunny dimwit.  Of course, his excruciating awkwardness in ROLE MODELS may have been even more astounding... dude's just great.  This thought also always brings to mind Brad Pitt's former-dork cameo performance on "Friends" - that man has never been a dork and, though IMO he has never before or since looked better than in that episode, I completely believed his character had long been a conventionally-unattractive dork.