Do not overrate what you have received, nor envy others He who envies others does not achieve peace. - Buddha
What it is
Envy is the desire for others' traits, status, abilities, or situation.
Why you do it
Because other people are so much luckier, smarter, more attractive, and better than you.
Your punishment in Hell will be
You'll be put in freezing water.
Associated symbols & suchlike
Envy is linked with the dog and the color green.
In the Summa Theologiae, medieval theologian Thomas Aquinas said of Envy: "Envy according to the aspect of its object is contrary to charity, whence the soul derives its spiritual life... Charity rejoices in our neighbor's good, while envy grieves over it." (2, 36, ad 3)
The Travelers' Guide to Hell says that Envy is ruled by the celestial sign of the Moon, and is "the key behind every advertisement." Incidentally, this book actually mentions the Seven Deadly Sins Homepage. All your friends are buying it. Imagine the embarrassment if you're the only one to miss out!