The context of the following conversation is Casey was thirsty, so they poured themselves a glass of water and took a sip.:
Casey says I'm really thirsty.  Do you want anything?.
The friend responds No, but you go ahead..
Casey responds I'll just pour a glass and have a sip of water..
The friend responds Drink up.  I'd tell you if I were thirsty..
Casey responds It seems kind of rude..
The friend responds Don't be silly; it's not like you're drinking in front of someone who's dehydrated in the desert..