When you say things like “you come across as condescending”, the author can feel hurt, because the story in their mind is that a friction in this one interaction is seen as an inherent flaw of the author or of their writing. Hurting your interlocutor’s feelings can actually further sabotage constructive communication, if that is your goal.
I’ve found more success by communicating my own feelings as directly as possible, without theorizing. For example, “When you asked me a question about my area of expertise, and then dismissed my advice, I felt disrespected, because it makes me think that you never sincerely wanted my help in the first place. Do you?”
While I'd strongly prefer that colanderman not be offended, given that he was offended, I'm glad that he voiced his offense as bluntly as he did. Yes, it hurts to think that my writing is that unclear, but I've got to own the audience's reaction even if (especially if) it's not the reaction I was aiming for.
I’ve found more success by communicating my own feelings as directly as possible, without theorizing. For example, “When you asked me a question about my area of expertise, and then dismissed my advice, I felt disrespected, because it makes me think that you never sincerely wanted my help in the first place. Do you?”