He sounds like an ISTP to me.
I have a (supposedly) ISTP friend who's type I couldn't determine for awhile.
The T/F dichotomy was particularly puzzling, but then suddenly it all clicked together. With some people it can be quite obvious, when it's not I use the following technique:
I think about their behaviour in a group setting: with team of their coworkers or classmates or group mates, not their friends though, because that's different. Feelers seem to be way more dimplomatic with people, they are not likely to openly oppose anyone, they care about maintaining pleasent atmosphere and feel very uncomfortable when someone dislikes them. Normally they won't mock people, they're jokes will be very mild and aimed more to make the relationship warmer than to show how witty they are (except maybe with their friends who they know are not going to get offended). Thinkers can sometimes mock somebody or be open about despising them.
It also seems that when Fs are not well-liked in a group of people they will feel like there's something wrong with them, while Ts are more likely to show "they are all idiots and who needs them anyway" attitude.
Hmm this seems so clear and simple in my head, but somehow I can't quite explain it right... I hope it makes sense.
Also to give you some clues, my ISTP is very competitive and playful, can be passive aggressive (she will hardly ever be open about being frustrated, or angry) and she likes making fun of other people a lot (A LOT) sometimes even in a mean way, but will feel very hurt when someone makes fun of her, even if it's not really mean. I suppose those are the charachteristics of the type not just my friend.