Originally Posted by Refiner

My $0.02 also is he is drinking far more than you think. IMO, he most likely has been drinking steadily (unbeknownst to you) and has built up a tolerance that he appears "normal" then when in a situation where he "has permission" to drink (e.g. a party or with others who are drinking) he piles the alcohol on top of the alcohol already in his system and becomes the weirdo you speak of. Not everybody gets falling down, passed out hammered. He is still trying to be functional like he always is when he's secretly drinking (but not over the top drinking) but neurologically can't handle it when it becomes over the top - hence the incoherent sentences, eye batting, head bobbing, etc.