This seems to indicate a utility function of something like:
(caring factor)*(friend happiness)+(happiness bonus)-(personal unhappiness).
Most of the time, the caring factor is so small that the happiness bonus dominates over, but when a friend asks a large favor that helps this person gain a large amount of utility, the caring factor overrides the personal utility lost.
This seems to indicate a utility function of something like:
(caring factor)*(friend happiness)+(happiness bonus)-(personal unhappiness).
Most of the time, the caring factor is so small that the happiness bonus dominates over, but when a friend asks a large favor that helps this person gain a large amount of utility, the caring factor overrides the personal utility lost.