Gp probably meant on the social dance floor which is generally considered to be taboo, and doing so is a mark of either a jerk or a noob.

It really is surprisingly infuriating.

A good friend of my wife once did this to me at a wedding. She had started a pair dancing hobby maybe six months earlier and was very enthusiastic about it. When I asked her to dance, I didn’t mean I wanted a lesson. It was so out of sync with my expectations that I left with barely an excuse in the middle of the song.

I just remembered I did recently ask someone to teach me a dance ("just off" the social floor), but 1) it was in a crowded bar just off the dance floor so it's less in the way than the onlookers 2) it is a notoriously easy dance 3) she knew I was good at dance 4) I picked it up in 45 seconds 5) we immediately went on to the dance floor and finished the song together with no further instruction.

So there are exceptions to the rule