Apparently, some flight attendants get annoyed when people ask for a diet coke! This makes sense though:
The pressure in the plane cabin affects all soda, but none so much as Diet Coke.
Flight attendants have to sit and wait for the bubbles to fall before they can continue to pour Diet Coke.
They will often get it started and then take the drink orders, while they wait to finish pouring the diet coke.
Now I feel so bad!