Comment by gfodor

Yep this is what I say too. The easiest way to prevent this kind of thing, and a large class of similar reactions, is to cast yourself as the 'incompetent nitwit' and speak accordingly.

As a bonus, in the cases where you are the nitwit (often in my case) it saves your teammate from having to do the awkward dance of the inverted problem of the OP: pointing out you are in fact, wrong, without it being taken harshly. If you already tee it up that you are probably incorrect, they can just run with your assumption in the common case where it's a correct assumption :)