I think he means:

  1. Have a root node R with 20 comments at varying depths
  2. Be reading comment 12, 4-5 layers deep
  3. Realize you don't like the entire direction this thread,
     rooted in node R, is going, try to skip ahead to the next
     thread in case it's more interesting
  4. Today, you have to click parent 2-3 times, or just page up,
     then collapse the whole thread

I find myself doing this fairly frequently, too. The existing tools are nice, but it's not that infrequent that I decide the car crash I was initially interested in is not, in fact, a good basis for discussion; at that point I want to see if the next root node has anything good.

Not the original poster, but if it's what I'm thinking it is: You're reading down a long thread and you've decided you want to stop reading and go on to the next thread. You have to scroll back up to the top most comment for that thread in the post to collapse it.

It would be handy to have a way to collapse from the top most comment easily from wherever you've scrolled down into the guts of the thread.