You were angry because you fundamentally trust people and he violated that trust. You fundamentally trust people because very few people violate it. Would it surprise you to learn that most people fundamentally trust which is why society works? This is why cheats and the like are shunned - you were witnessing your own little piece of societal breakdown. That is why you were still polite: you're hardwired to be helpful and friendly to others who are helpful and friendly. I could list off a shelf-full of books describing why humans trust each other and the clinical tests that prove it. What this means: don't abandon your worldview. Recognize that it was tested and that the responses garnered were 100% appropriate and that's what makes the world go round.The whole experience- and similar ones I've had- just made me angry. I like to believe in the power of good community and faith in fellow man and charitable acts, and situations like that sort of destroy the illusion.