...living on planet earth, giving you 80% of the crap you gave me seems about right.
Consider the consequences if everyone follows your rule. Assume someone gives you one unit of crap, possibly accidentally. You respond with 0.8 units. (It's hard to measure this precisely, but for the sake of argument let's assume that both of you manage to get it exactly right). He, in turn, responds with a further 0.64 units of crap. You respond to this with 0.512 units.
This is, of course, an infinite geometric series. The end result (over an infinite time period) is that you recieve 2 and 7/9 units of crap, while the other person recieves 2 and 2/9 units of crap. He recieves exactly 80% of the amount that you recieved, but you recieved over twice as much as you started out recieving.
If you return x% of the crap you get (for 0<x<100), and everyone else follows the same rule, then the total crap you recieve for every starting unit of crap is:
%5E2%20}%0A)
This is clearly minimized at x=0.
Alternatively: he could notice that he gave you 1 unit of crap and assume the 0.8 units of crap you gave him is an equal penalty.
If someone yells at you, you're likely to respond - but if someone yells at you because you just pushed them, you're less likely to respond.
Here's the new thread for posting quotes, with the usual rules: