> it sounds harsh to say "I don't take meetings with no agenda", but is the right thing to do
Evan's is the wrong way to do it. "I am busy–do you have specific recommendations you can share over email" is more concise, polite and to the point. (Ignoring the e-mail, or a simple not interested, are also options.) And if you want to use those words, fine, but leave off the "low effort" insults at the end.