My favorite ones are those that do their very best to run the timer down as long as possible.
It's really a normal reaction for a person who has a competitive personality to be upset at RNG or a misplay, but saying things like that is just a sign of immaturity.
As far as what one should do, the answer is be polite(smile, nod, say hello, give them a high-five, whatever people do in your area). How much it matters? Not very much, all things considered.