When you agree, and pretend to believe someone when they are obviously lying, to avoid the awkward situation of calling them out on their claims.
Usually about something trivial, but could be about anything.
Guy 1 : DUDE! I just got into a fight with 10 people and laid them all out.
Guy 2 : Wow, it doesn't even look like you got hit...
Guy 1 : That's because I was too quick.
Guy 1 : (I shouldn't have given him that generosity belief.)