I remember a colleague (note: not boss, just a colleague) who was constantly "assigning" work to random people in the office. He tried it with me. I just took his "assignment" memo, the one he wrote up after I said "no" orally, crumpled it up and tossed it in the wastebin. "No means no."

I can't fathom what goes through the heads of these people other than, I don't know, a lot of echoes from the empty space.

Stay strong in the meeting. Continue with "no". It's a word men need to hear more often from women.