After an hour of extensive googling, I think I might have stumbled upon an answer.
Gintoki screaming Psycho Pass! when hit by the chair,
is a reference to a scene from the Psycho-Pass series, where Kasei gets hit on the face with a book, thrown by Makishima.
Gintama is well known for using gags and references regarding other animes. Most references are made when the situation is similar to that of the other animes. This Psycho-Pass reference is a new one.
I also believe it could be a word which was misheard by the viewers. Found this on Yorozuya Soul Forums. The author has a good point.
Gin had shouted a lot of random words before, when he gets hit or blown away, maybe it's just a random thing, I personally think that maybe he actually said "psychopath" but the translator though he said Psycho-Pass, since they are both pronounce the same way (Psycho-Pass is a pun), at least that's my assumption, I could be wrong, it's not like I'm fluent in Japanese(YET!)