Watching the video brought back memories of hearing about (and thanks to YouTube, in one recent case, seeing) Harlan Ellison's past escapades. He has for decades been the "bad boy of science fiction." Yes, he's a great writer; yes, his work has been to some extent ignored by the mainstream because he worked in spec fic (even though he gets mad if people call him a science fiction writer); yes, he is, in fact, a genius. Equally clear is that his ego shines through his public performances every bit as much as his talent shines through his work.
I don't buy the argument that being a genius gives you the latitude to behave like a jerk. It's not like every great writer does. Look at Neil Gaiman, Joe Haldeman, Nancy Kress, and Connie Willis—all known for unfailing politeness to fans and fellow writers as well as the excellence of their prose.
Maybe Harlan Ellison is just insecure where they are not.