Let me see...
It might have been established he's INTP (by INTPs, I suppose
), by I disagree.
Firstly, Bernard is 100% N (not ISTP for sure), because he lives only in his head and absolutely sucks with reality. Manny's and Fran's characters, who are most likely both SJ, are designed to keep him functioning in reality at least a little. I'd say that especially Fran is designed to be almost his polar opposite, which is one of the things that leads me to think he's INFP. The owner of Goliath's books was blatantly a caricature of an ESTJ, and Bernard is (in my opinion) blatantly a caricature of misanthropic, choleric and absolutely incapable, but also somewhat 'honorable' INFP, that's why their interaction was so funny.
Furthermore, he's repeatedly shown that he's got very strong values (as eccentric as they may be), and he's obviously a very romantic and idealistic dreamer, who ridiculously idealizes all his ex and future girlfriends, which is also a caricature of typical INFP behavior (e.g. the episode with his 'summer girl'
). He's also somewhat artistic (e.g. the episode where he and Manny were writing the children's book
), which also seems to be rather a caricature of NF than NT.
You might say that all these things are possible for an INTP as well, but you have to keep in might that's he's a caricature and all typical traits of a certain type are parodied in him. And I would say these traits are INFP traits, not INTP traits.
Plus, if he was an INTP, he would have to be Ti dominant, and I haven't spotted any sign of Ti in him in any single episode.
There's nothing rational in the actions of an misanthropic INTP, trust me.
That's possible, but there's nothing (as in,
nothing nothing) rational in the actions of a misanthropic INFP, don't you think?