The initial photos posted, esp. photos #2 and #4, convey a typical ISTp look... After looking at several clips, (below,) I realize that these are not typical expressions for him. (I've never seen any of his movies.)
In the initial interview posted, I attributed his 'internal tension' to excitement, i.e. from hosting SNL. The male Si-ISTp can act very much like this when excited, but only for short periods. After watching a few more clips, I realized that Shia LaB sustains this behavior... He's jittery.
Here are two clips that say a lot:
http://youtube.com/watch?v=2ElFiiNfuyQ
Compare his behavior/humor with Ben Stiller's, (ENTj
http://youtube.com/watch?v=0LhWKxxWyWw
DiscoJoe has it right here, I believe. ENTj...
JuJu, I see what you mean about the jitters. The pics I posted are typical of any other I found of him. I think there seems to be a disconnect between his public persona and private person (not that I would know for sure, of course). Anyway, thanks for the replies so far....