Not sure how useful this is or whether others will agree but consider the follows:
Overconfidence is all about the person having an unrealistic view of his/her (will be sticking to 'he' here on out) own abilities - namely overestimating his abilities and failing to recognise (at least outwardly) the limits of his own competence. Everything else is entirely up to you.
Now, maybe I'm reading it wrong but from the sounds of it, your major struggle is in figuring out how to make him not abrasive or unlikable; to make him overconfident without being douche. To which, I think doing the following would help:
1. Make sure his unrealistic view is purely about himself. It's not that he thinks others can't do a certain task but rather he feels that he is the best person to do it.
2. Have his heart be in the right place. It's not all some ego trip for him. He honestly and truly wants to help.
3. In the event he fails to accomplish something he set out to do (especially with others having to clean up his mess), have him disappointed/embarrassed/distraught with himself. Not because he realised he isn't as good as he thought he was but that he had let others down, inconvenienced them and/or put them in danger/exposed them to trouble.
In summary, 'overconfidence' is generally seen as an unlikable trait. So, your character will probably need a few positive traits surrounding his overconfidence to compensate for it in order to avoid its negative connotations. A good/possible example to look at is Fred from Scooby Doo.