No (drinkable) beer is actually "flat" despite what some from abroad say about English bitter. I will brew bitters and serve them from a hand-pump (to some, the pinnacle of "flat" beer!) but I still add priming sugar to the cask and would cry in my pint if it really was "flat".
Now bottled beer is another kettle of hops (did I say that right?), you'd definitely be expecting some life in that!
The homebrew world now often talks in "volumes of CO2". How much CO2 is dissolved in the beer. Shortly after fermentation you can expect beer to contain about 0.9-1 volumes of CO2 dissolved in the beer while it is just sitting in the bucket. My priming (in a cask) might push this up to 1.2-1.3 volumes (that will show up as less that 4PSI in the cask). Without it my beer would surely be lifeless and "flat". With it you wouldn't be using words like "fizzy". If you put a lot of priming in the beer you could get 3-4 volumes of CO2 in the beer. Now you can use the "F" word to describe that!
But bottled beer is a different... (kettle, hops?). Get the priming sugar/drops in there! You'd be looking at 2-3 volumes of CO2, but it would be quite nasty without it. And if your mates are opening the bottles and they don't go "ffsss" they'd likely put them to one side!
