hair envy:

A feeling of envy regarding someone else’s hair. Can be an envy of the color or length or of the ability, for example, to easily go from curly to straight.

• You cut your hair, OMG you are so giving me hair envy right now!
• Ugh, does she have her own stylist? She always gives me hair envy!
• Can’t talk right now, working on my hair envy.