Jealous people want what others have desperately, but have no belief in their ability to get it. They believe everyone is against them somehow, and that is why they don't have what they want.
Jealousy is a type of victim mentality. They always have a finger pointed to blame and play on peoples empathy because of it.
Jealous people will pretend to be your friend until you don't help them get what they want or you hurt them in some manner. Once you hurt them, they will make sure that everyone knows what a "mean and cruel" person you are. They will talk about you to others, but will not come to talk to you. Jealous people have this underlying emotional need for people to notice their lack, and do something about it for them.
The problem with having a friendship with people who are jealous is that you never know what might trigger their jealousy. Your job promotion? Your new car? Your recognition by someone very important? A new relationship? You will not know until the trigger is pulled.
Most likely, the jealous person grew up with a lack of some kind. Maybe their parents were poor and couldn't afford things, maybe poor financial decisions caused them to lose all they owned and they needed to start over, or maybe they just want things others have without having to work to get it (aka, the seemingly easy I deserve it, route)
One obvious sign of a jealous person is they cannot be genuinely happy for you when good things come. They will talk negatively about you acquiring things you don't deserve or insinuate you cheated the system to get it. Jealous people will even think that you are somehow "favored" by God and that is the only reason you have, and they have not.
Jealous people often like to turn their jealousies into competition. If you get 'this' they must one-up you and get 'that!' Jealousy is cruel. The bible says "Jealousy is cruel as the grave: The coals thereof are coals of fire, Which hath a most vehement flame. Song of Solomon 8:6 They may even insinuate that the only reason you have what you have is because you are a "workaholic."
If you have friends, acquaintances, co-workers who are jealous, stay a short distance from them. A jealous spirit is toxic. Never respond quickly to their comments. Practice your responses ahead of time. You may already know they will make a rude comment at some point about your new promotion, or your new car or your new relationship.....be prepared.
Again, set your boundaries. Be humble about your blessings no matter how deserving they are. Let go of things that don't really matter to you for the sake of ending the battle early. Jealous people have no problem being vocal, so end it early. Compliment them when you can, it will help to lessen their insecurities. Don't retaliate with criticisms. And do not feel the need to apologize for your strengths or successes.
Lastly, hang around those who know you, and they know your motives and they know you deserve all that you have, and can celebrate with you.
Adapted from "Difficult Relationships" by Luke Gregory