The 7 deadly sins, were first introduced by a Greek monastic theologian Evangrius of Pontus when he drew up a list of eight wicked human passions: Gluttony, lust, avarice, sadness, anger, acebia (from the Greek word asevia that means to have no respect), vainglory and pride.
In 6th century St. Gregory the Great reduced them to seven, changing vainglory into pride, acebia into sadness and adding envy.
Then Th. Aquinas suggested in 13th century that the seriousness of the sins could be ranked in this way: Pride, envy, anger, sloth, avarice, gluttony, and lust.
As per Dante’s Divine Comedy the seven deadly sins are: lust, gluttony, avarice, sloth, anger, envy, pride.
These impulses are still characterized as "deadly passions" rather than sins in and of themselves. Instead, to invite and entertain or to refuse to attempt resistance against these passions is considered sinful in Orthodox Christian moral theology.

Do you think that you could add or reduce some? What is your ranking of the sins seriousness?