The Prisoner's Dilemma. Classic, classic example where cooperation has a non-minimal cost - ie, the risk that they will defect against you, multiplied by the probability that they will defect, is the cost of cooperating.

VERY minimal cost (if any) of cooperating with a cooperating entity

And in the Prisoner's Dilemma, if you somehow specify the other entity is cooperating, then cooperating with a cooperating entity carries a cost still: the difference between "both cooperate" and "you defect against their cooperate" is the cost of cooperating there.

throwing cryptic opinionated darts

If your argument rested on some mathematical concepts, and one of them was an equation that you derived incorrectly, and wedrifid pointed that out, would he still be throwing darts? He wasn't telling you that you were wrong because he hates you, or because he enjoys ruining peoples' time on this blog, or any other sadistic personality trait, he was pointing out the flaw because it was flawed.