When the human race has been decimated by a zombie virus, even the survivors can be your enemy.
DayZ is an open-world, survival horror game set in the fictitious post-Soviet state of Chernarus which has been decimated by a virus that has turned most of its inhabitants into zombies. The survivors have to scavenge for food, water and shelter — all while trying to avoid being eaten by the undead. With all that pressure, you’d think other survivors would give a high-five in solidarity. It’s not like you’re asking for ammo or a book of matches.
Considering how mean anonymous users can be while playing an online multi-player game, flipping the bird is not even that offensive. Many players would have probably just shot him and taken his weapons or anything else that could be useful. If you have a bleak view of humanity as a whole, this short clip is a pretty accurate representation of what most people will be like if society collapses.