Apparently, this is what happens when you mess around and leave Apple Remote Desktop running on one computer connected to another, and then go on the computer you are controlling and accidentally try to control the one that is controlling the one you are on. Did you get that?

What you have here is what we call the Apple Remote Desktop Vicious Vortex Death Spiral…of Doom.

I tried to close it, but to no avail, each and every sub-window had to redraw and refresh everything I was doing, and I was getting nowhere fast. I was finally able to minimize the Remote Desktop window on the original machine (iMac)  from the second computer (MacBook Pro) and then Forced Quitted ARD that way. All was then well.

Be careful out there.