I think one of the biggest ones that no one has mentioned yet is to have the ability to laugh at yourself!!! Because at one time or another (probably multiple times) you will be the subject of a joke or funny story of some kind, and it helps to be able to laugh at yourself.... I think also most flight attendants develop a very black, dark sense of humour - you start to find the nastiest and weirdest things funny! I think its a coping mechanism - some of the stuff we see and deal with can be just horrendous, so laughing at it helps us deal and "not internalise" as someone else already mentioned...
(of course, I dont have one of those dark senses of humour - I am perfectly angelic and pure *cough cough* 
)