If you've ever wondered why it took so long for a flight attendant to reach you with your drink order, it's highly likely that someone slowed down the process by ordering Diet Coke. Those who are thirsty and in need of a quick drink don't usually opt for Diet Coke on the plane.
In a 2013 blog post on These Gold Wings, a flight attendant mentioned that pouring Diet Coke took more time compared to other drinks on the plane. This is why attendants dislike serving Diet Coke during flights. Due to the average airplane compartment being adjusted to the equivalent of about 8,000 feet above sea level, liquids, including soft drinks, tend to foam up more when poured out from a can.
Flight attendants have to wait for the bubbles to settle before continuing to pour. If three passengers all request Diet Coke, the attendant usually takes another three drink orders, serve those first, and then proceeds with pouring the Diet Coke.
The veteran flight attendants have a trick for pouring Diet Coke on the plane. They completely turn the can into the cup and then lift it up at a slight angle to pour the liquid more quickly without causing excessive foam to spill over.
