I find the exact opposite, most people...and yes even fellow passengers are normally nice to each other.
OK you get the odd DYKWIA, not only on planes but other places too.
The behaviour you described is appalling, it takes a really 'special' person to put themselves before a medical emergency.
As far as breakfast (or any other onboard meal) is concerned, surely it is well known that you may or may not get your first choice.