The term "air mattress" is often used - at least in gay circles - to describe a male stewardess.
Gays who fly on holiday often refer to a male stewardess as an air mattress. There does not have to be any malice behind this designation. Nevertheless, it is a rather discriminatory term that is often compared to the female stewardess's counterpart, the "juice pusher".
Whether "air mattress" at this moment is meant to allude to the rumour that flight attendants like to sleep with the pilot or whether the whole thing refers to the upcoming holiday and the air mattresses that are often used is not really clear. What is certain is that this designation is unfortunately a disparagement of a thoroughly exciting profession.
How the steward in question ultimately deals with being called an "air mattress" depends, of course, on his individual character. Especially when he also gay it may even be that he can laugh at the term. Just as with regard to the so often quoted "Drama Queen" or the "Clamp sister" it does not have to be a direct insult, even with the air mattress.
How this name is to be assessed depends essentially on the circumstances, the "sender" and the manner of address.
Stewards who are equipped with a healthy dose of humour here will be familiar with this term and - if it is brought up in connection with a flirt or a funny saying - will certainly not put it on the gold scale. However, anyone who plans to invite the nice flight attendant to dinner or to get to know him better should think carefully beforehand whether he should actually enter into the conversation with a "Hey, air mattress!". Surely there are alternatives that are far sexier...