Why on earth would you get him to do the cognitive functions test but not an actual MBTI test? Do you enjoy mystery? Were you trying to conceal your intense interest?
How old is this guy? How well do you know him? Do you get any chances to watch him interacting with other people?
To be honest, your description of him is just too vague and resembles just about any given smart, polite person on a good/bad day. More information needed!
<doubts, second guessing doubts, and list of "me"s>

JJJ, your post made me chuckle.
I didn't get him to do an actual MBTI test as I do not know of a reliable free site.
He is in the late 20s - early 30s range. My observations was based on watching interactions. If you have more questions to ask, it would help, as I do not know what information would be relevant or not.
These are negative traits I've observed in him:
Stubborn; overconfident at times; occasionally overlooks Se detail; resistant to group affiliation and strongly independent, yet feels lonely and distant; doesn't ask for help when needed; feels "different" from others; doesn't always vocalize thoughts out of experiential frustration and/or sympathy; enjoys systems sometimes more than people.
As a child, learning came naturally, so he took it for granted. But he buckled down once he realised he had to earn a living.
No. Maybe many INFJs will, but I've met several INFJ guys who won't, at least until you're far far inside their defenses. I still don't think he's INFJ, but the picture drawn fits my experience with male INFJs much better than my experience with male INTJs.
The main difference is that then you see that one is T and one is F. Many INFJ guys don't show much of the F before you get beneath their skin, so they end up looking like Ts.
Ever heard of the warm and fuzzy theory (probably called something completely different really):
As for the edit being unfair: I did it right after posting before there were any replies, so if you hadn't been so eager on stalking your own threads and wearing out your F5, it would all have been good.

at theory.
How would a learnt INTJ, or say, an INFJ morphed to INTJ, be different from a blue-blood INTJ?
Yes, how could you tell my f5 is worn out.
Also, I think your guy is INFJ also, a very mature one too. INFJs can give the illusion of being more mature then they actually are, until you get them to open there mouth and they say something completly off the wall. It's a good measure, not if they say something off the wall, because I assure you they probably will, but what they say.
Basically what I'm trying to say is aelen, to take that horse to a quiet field and ride him.
What would be some off-the-wall things, that is different from say, an ENTP rambling?
And no, *cough* no riding.
Have you considered the possibility he might be an ENTJ instead?
So far, he looks like an xNTx, a young one (no well developed tertiary).
Hi Blackmail! Not ruling out any possibilities, was just opening it up for discussion, but so far, the vote looks split between INTJ, INTP, INFJ, mild ENTP tendencies.
Why I never thought ENTJ, was because there was never that overt "lion" influence from him. Folks gravitate to him, and he does intimidate some, but the influence stems from an innate restraint, vs an overt control.
No fun, so do you like this guy or what?
Was your thread title a double
entendre or not?
Edit: if you *do* like him, don't let these MBTI mongers dissect him to shreds before he can let his true character reveal itself.
Aheeee. NF weighing in.

I like him in as far as I find him interesting. If I loved someone, the type wouldn't matter.
Right now, all I'm keen in is to try puzzle out which type, or what is the best fit type, the board's eyes would see him as, as I'm stymied by the fact that someone of such a clear character, can be so hard to type.
Perhaps I missed some clues myself for e.g. Or never realised some facts. It is why I've been asking for questions, and a discussion of reasons why some are guessing which type, vs hard conclusions.
I'm gonna go with INTJ, too.
Rationale? And welcome to MBTIc.
