Expect debate. INTJs enjoy tearing things apart to understand them and to prove (or disprove) their worthiness.
They will gladly argue a point they don’t actually support, just for the sake of argument or to probe things. This bears repeating: an INTJ can easily and persuasively assume a point of view which is wholly contrary to his actual conviction. If in doubt, ask.
INTJs do have a strong sense of humour, often dry and quick, but also a bit warped. It can easily take a morbid streak.
Expect blunt, honest, sometimes even hurtful answers: if you don’t want to hear the truth, you wouldn’t ask, would you?
INTJs like to do lists, enumerations, pattern sorting and putting things into an ordered state (ordered for them, not necessarily for the rest of the world).
Statements you can’t back up with either solid facts or solid reasoning will at best be ignored and at worst poked fun at in ways not many people would describe as nice.
Try to be both concise and precise. Using 81 woolly words where 18 sharp ones would suffice will not endear you to them.
They do love wordplay though: if you can re-package your 81 woolly words in a witty, unexpected, esoteric fashion, they’ll appreciate that.
Don’t expect an INTJ to respect anything you (or some other authorities) say just because you (or some other authorities) say it. INTJs bow to one authority only: rationality.
For an INTJ truth is more important than simply being right, so they will readily admit errors or mistakes (once they have been convinced something they said or did was indeed wrong — to convince them may not be easy though). INTJs unfortunately expect others to work likewise (and react bewildered if they don’t).
Stick to a statement after being proven wrong by facts or reasoning and an INTJ will treat you as an irrational idiot and everything you say as probable nonsense.
Try not to be repetitive. It bores them to death.
Clumsy attempts at political correctness and similar aberrations will greatly amuse them.
Don’t be surprised at sarcasm, hyperbole and flippancy. In fact, a non-sarcastic INTJ must be severely ill.
Expect punctuality and exactness. They try hard to be on time and they hate unpunctual-ness, especially of the casual sort: the words obsessive-compulsive come to mind.
They tend to be quite forgetful in everyday life, especially for trivial things like car keys, dropped tools or anniversaries.
You can’t trust that an INTJ takes something, anything for granted. They do take some things for granted, but you’ll never know what and what not. The more extreme ones are actually willing to put everything to the test (and I mean everything).
Remember that INTJs believe in workable solutions. They are open-minded to all and every possibility, but they will quickly discard any concept they deem unfeasible.
Their way of showing that something you say (an idea, a suggestion) has potential or merit is by trying to pull it apart (which shocks those poor souls who instead expected awe or admiration). The ultimate INTJ insult to an idea or suggestion is to ignore it altogether, because that means it’s not even interesting enough to deconstruct.
INTJs can and will make themselves and everything else (and again, I mean everything) the butt of their jokes, witticisms and deeply nonsensical remarks.
Do not expect INTJs to care very much about how you view them. They already know that many people see them as arrogant bastards with a weird sense of humour and they long since got used to it.
INTJs, in the privacy of their minds, frequently think the unthinkable and expect the unexpected. So don’t be taken aback if they express little or no surprise if something “impossible” happens.