I met Harlan at two conventions in St. Louis, Missouri, in the late 1960's. I did not happen to see his angry side.
WorldCon 1969 was in St. Louis. Harlan was there, as he had been at a smallish local S-F con the year before.
At St. Louis Con he was peddling a fanzine-like booklet titled "The Kong Papers." On the second day of the con (I think) they screened King Kong in the main meeting room.
When Kong killed the T-Rex, from the back of the room came a huge yell of "Yea Kong! Yea Kong!!" It was Harlan, of course.