I'm an INTJ, too - and relationships are our Archilles' heel because INTJs have extremely high standards. It's not about being "irritable"; I don't have many close friends because when I do make friends, they all end up disappointing me, sometimes even upsetting me because they act in ways that I would never do! Also, I don't like when people "fall apart"; don't get me wrong, INTJs can be very emotional and fall apart themselves, but it's done in private, behind closed doors. Public emotional display isn't something that INTJs tend to do. Similarly, small talk isn't something that we tend to excel at, but I've gotten very good with faking enthusiasm. So yeah, it's hard, when I see people dating and getting engaged and think "I'm still single, why?" I don't know what to tell you, but some of the friendships that I've had have been with scientists/PhDs (not really surprising when I think about it!)...so maybe we INTJs need to spend time hanging around science labs!