>>gregor+(OP)
Are you talking about the tit-for-tat strategy in the Prisoner's Dilemma? That's a particular toy model with an exaggeratedly punitive payoff matrix. But not every daily interaction can be reasonably mapped onto that matrix. A random interaction with a brusque stranger in a queue isn't necessarily going to result in a good outcome for your being rude ('defecting') in a tit-for-tat. If anything it might cause you more stress and embarrassment than if you'd remained mum.