My first buy point for more S&P 500 is 20% down.. who's with me?
As I'm in the withdrawal phase, I don't have much cash, but I'm in.
I did go all in at 20% down in September 2008. Watching the further drop was painful, but I kept throwing new cash in until I ran out (but still kept 401k DCAing).
Last major buy was February 2009 1 share of BRK.B at $2400, mostly for the shareholder's meeting badge.
Retired now, so it seems to have worked out OK.