In the movie, "Devil's Advocate", Al Pacino as the devil says in one of the scenes, "Vanity ... my favorite sin". 

We don't believe that vanity is a sin. Without some level of vanity, a person does not care about themselves and that's the beginning of the erosion of self image.

Controlled vanity is a good thing because it makes you feel good about yourself. And feeling good about yourself dramatically increases your value to others.

Pity the couple that says "I'll take care of you if you take care of me". They have it all wrong. It should be "I'll take care of me ... for you, if you take care of you ... for me".