[*]He's a sensitive guy. He gets his feelings hurt easily and has a nurturing nature. We often refer to him as the "mother hen" behind his back.
More likely Fe than Fi, particularly if he tells you about his feelings a lot (enough for an intp to notice very often!)
[*]He writes poetry but is loathe to advertise this fact.
Since he doesn't exactly seem shy, this again seems more like Fe than Fi > more concerned with other people's impressions of him than wanting to reveal his inner self.
[*]It sometimes seems like he is primarily motivated by what others think about him. For this reason, he says and does things to impress those around him. And if he can see that you're not impressed by his story or his antics, he doesn't stop...he tries harder and harder (becoming more annoying by the second).
Points to a stronger F than S perhaps, Fe in particular - his need to be liked and accepted and to try to push himself on people to attain this appears to override his awareness of when this approach simply isn't working. ESFPs, at any rate, are typified as the class clowns because they're generally
good at it through being "in the moment" and able to respond quickly to the signals they're getting. This might be more FJ behaviour again.
[*]He's flighty. He just drives around and finds people to be with (and get food with) all day long. He suddenly decides to go here or there at the drop of a hat.
Extraverted (can't stand being alone)
Any type's car can be messy

It's too easy to put that down to p-ness - some J types are the messiest people I know!
[*]He wants to go to culinary school.
Being a practical career, it might
perhaps suggest S
[*]He doesn't really work.
Not surprising with the energy he appears to put into failed socialising!
[*]He doesn't have a mean bone in his body.
Strong F, presumably
[*]He is awkward with girls. He likes to flirt very overtly, and is not afraid of asking a girl out, but he just always gets rejected. They often refer to him as a "creep."
Extraverted anyway, and clearly not very flexible if he can't change his approach in response to it not working. Again I think this hints at J, and maybe a bit of FJ denial...
[*]In social settings, he is effusive and manages to talk to everyone (sometimes all at once).
Extraverted anyway
[*]He can't be quiet for two seconds. Usually he is talking nonsense and being silly.
Again, extraverted *not to mention attention seeking*
[*]Did I mention he is very very silly?
Not sure how type related this is given his tendency to try to please people - it may be part of his attention seeking pattern. Might suggest P-ness, though this goes against the general impression somewhat.
Probably the F tendency to want to see the best in people at any rate. If it persists and is part of a scheme of trying to deny how people really are, it probably points more to FJ again.
[*]In social settings, he is concerned that everyone be included. He doesn't let anyone feel left out.
Very much an Fe tendency, particularly noticable in E_FJs
[*]He's not particularly clever. It seems like him and I are on two different wavelengths. I often have to stop and explain my quips to him.
Intelligence can be rather subjective, but this may point to weak N given your own type *and what you say later about your brother*
My first instinct was to say ExFP, but on reflection the evidence points more to an E_FJ type. The strongest positive evidence always seems to be for extraverted feeling to me. Neither his intuition or sensing seem that well developed, which might be the key to the bad impression he keeps making - he gives the impression from what I've read of being
all about interacting with other people, without really much of a solid secondary to fall back on. This goes quite well with what comes across as his extreme *though feeling-modulated* extraversion.
In short, an E_FJ (I'd perhaps lean more towards ESFJ) with strong extraverted feeling and a real need to develop his other functions to establish a more secure sense of self, and maybe
earn the personal regard and affection he seems to crave above all else.