Do you find you ask others a lot of questions for the sake of stimulating conversation? Usually, I know the answer the other person is going to give, but I just like to focus my attention on the other person and keep the conversation going.
Also, on a bad day, I find myself to be quite misanthropic and critical of others in my own head without wanting to be. I rarely voice my negative opinions of others, though. Would you agree with this?
More often than not I do know what they're going to say before they say it, yes, and sometimes I'll ask questions to which I already know the answer just to keep people happy and to reassure them that I'm interested in what they have to say. I usually find I don't need to though, as the majority of people seem content to chatter away about anything and everything and require very little encouragement from me other than for the occasional smile, 'mmm' or 'yeah' to prove I'm listening. That usually works out fine, because I'm generally more of a listener than a talker anyway. The bottom line is: normally I'm quite comfortable with silence myself, but a lot of people don't seem to be, so I try to make sure they're not feeling awkward or ignored by asking them questions about whatever they seem to enjoy talking about. Most of the time I am genuinely interested as well, I like learning about people.
Yes for the second point too. They're rare, but on a bad day I feel completely isolated from the world and generally have a chip on my shoulder about everyone and everything. I'll start picking people apart, doubting their intentions, getting frustrated with individuals as well as humanity as a whole and consider a large number of people just plain 'stupid' or inferior... superiority complex to the max. Ouch. I never ever,
ever voice these negative thoughts though. People often don't even realise I'm
having a bad day, even though I'm feeling very melodramatic and depressive inside my own head. I suppose a part of me realises I'm going overboard and keeps it all under control. On a
normal day I'm honestly very accepting and see the good in everyone. I really hate the silent monster I become on a bad day, it's like I become an entirely different person at times.
You know you're an INFJ when...
you use

after every one of your arguments.
This one made me grin.

I don't know if I'd use that emote, but your point still remains. It's very rare for me to have an arguement with someone
without trying to keep the peace one way or another. Then again, I wouldn't say that I argue all that often anyway. It takes an awful lot to get me really angry, even when I'm defending something I feel passionately about.