You've no doubt heard it said, you can only be offended by someone if you allow yourself to be. That sentiment holds a lot of merit. It's up to us how we take things internally as they are inflicted upon us externally.
Same with jealousy. We can allow it to fuel us to reach higher goals than we would have normally set for ourselves, or we can allow it to trip us flat-faced into the pavement. Jealousy can also motivate us in another direction - retaliation, gossip or slander. It can transform us into a type of wild animal, out only for our preservation without regard to anyone else's well being. All we see is what we want, and go for it at all costs, even smearing those we are jealous of along the way.
What are some reasons that can invoke jealously? Briefly, a few reasons are: love, money and success. Slightly expanded examples:
1) A lover with a wayward eye (or at least what we perceive as such).
2) We know someone who has more money than us. We see them buying things we could never afford.
3) A friend experiences success in their career while we're answering phones, and stuffing papers into a filing cabinet.
How can we use this in our writing?
Have a character's personality change because of feeling jealous over something.
Have jealousy create conflict, or ruin a romantic relationship.
Use dialogue to support an underlying jealousy between friends. Oh, it must be nice to have an Ipod.
Have a character allow jealousy to consume them, maybe risk their career, family life, and possibly even their health.
Have a character slander another. Caution here is to use this only in a rare, special case. If you're not careful you'll quickly alienate your reader. Slander is not an attractive quality - at all!
These are just a few ways. What are some ways you've incorporated the human emotion of jealousy in your writing?