How can I deal with someone that is acting like a 'diva'?

I think it would depend on how well you know this person. If you are good friends and the person is just having a moment, maybe let them have it. They may be trying to get something out of their system. If they are someone you do not know very well, this may just be their personality, or they may also be having a moment and just need some time to get out of it. I would suggest trying to discern why the person is acting this way, but if it is really bothering you, you may want to find a way to leave the conversation.

You don't need to "deal" with anything unpleasant in life. Look at the situation, changes are that you can remove yourself from the situation, or limit exposure to the bare minimum; once a diva, always a diva (narcissist???); so, don't feed the monster and seek better company. Unless you want to self-sabotage your own life.

Give them a snickers... No honestly I guess you should try to talk with that person get him/her back to earth with honesty and in a calm manner.

There could be many different reasons why that person is acting in the way that they are. The best thing you can do is to try and stay calm, and recognize that you are bothered by their behavior. Maybe try addressing them directly, or going to an objective third party to explain the situation.

Try having an open, honest conversation using "I" statements. Saying things like "I feel ______ when you _____" and maybe give them some loving suggestions about how they can improve their relationship with you.