You know what, I actually think you should find talking to that co-worker encouraging ToeJam!!
It shows a reflection on them not you in the way they answered so......OK I know you have difficulties but at least you don't have the difficulties your colleague has on top of those!! From what I can see you're not insensitive, oblivious to people's feelings, judgmental, focus "full on" on the "negative" things you think you see in people, you're not persistent in stating what you think are faults in other people especially when the chance is there (which it was) to throw in good aspects as well.
And at the end of the day it was his perspective, that doesn't make it true. You say he knows you but does he know you. Often colleagues only "see" parts of us, and parts of us that can be out of context with the rest of our lives.
I mean you said it yourself "I think most who know me see the hard layer I guess I construct". YOU is much bigger than someone's "colleague" and YOU is much bigger than certain aspects people may "see".
If you want to use what he said as a positive tool in working towards changing things for yourself at work (and some of those things aren't going to take a lot to improve) then fine but remember those are just his opinions. And I'd completely agree with keeprolling that sometimes things/qualities can be put across as not "helpful" when in fact they can be very "helpful" in different situations.
Really sorry you were made to feel that way though and you didn't "let yourself down". It was probably hard for you to ask anyone, and something you really weren't used to doing right?? So maybe it was "a bolt out of the blue" for you??
As for the purpose of the exercise, it sounds like your T has left you a little in the dark on that one. BUT why not have a think about a purpose which might help you personally, doesn't have to matter about your T's.
For example you could use it to see how much of yourself you might actually be "hiding" from people. If they say you're.......but you're not necessarily then you might want to think how you could show them more of you, or why you don't want to show them more.......
Or you could use the positive comments to improve on the way you feel about yourself.
Or you could use it as an experiment in talking more openly to people about more personal things. For now use the exercise to help you, and hold onto the positive aspects you can find from doing it.
Best wishes
Alison