In Bones' defense, I thought the punchline was fine -- and funny. 
From my experience, a bipolar person will be a completely different person when she's in the manic state than when she's in the depressed state. It's not the extreme of an MPD, but the personality and behaviors will be different enough to be noticeable.

From my experience, a bipolar person will be a completely different person when she's in the manic state than when she's in the depressed state. It's not the extreme of an MPD, but the personality and behaviors will be different enough to be noticeable.