I was in a long relation with an INFJ, and one of my best friends is INFJ. I don't relate so much to the OP, if I had to give one issue that has gotten me in trouble with my INFJ's, its an inability to understand why they have had to be so serious or "heavy" alot of the time. I've also noticed that when I try to shake this, or lighten it up, they can tend to feel attacked by it.. and will sometimes twist it into me being shallow, unconcerned, and not understanding the longevity of the problem. At those times I just want to scream "NO, I get it! I really do... I also get that life is too short to spend worrying and wallowing. Snap the fuck out of it man!"