Lust

Lust is in may ways like Pinky Pie, she's hyperactive and a little ditsy, but incredibly devoted to her friends; the other Sins.

Lust unfortunately finds herself becoming trusting and attached to almost any pony she finds, she'll convince herself that they really like her and eventually work herself into a frenzy of love induced delusion.

Her friends have worked out that if they ever meet a new pony they will introduce Lust last and never leave her alone with anyone other than themselves.