I still don't think this is passive aggressive. It's an indirect approach. Passive aggressive, like Seesaw said, is a hostile behavior that masks anger. There is no hostility or anger here.

I cannot ask him directly if he likes to look in the mirror. That puts him on the spot and it is awkward. Seesaw's suggestion I think is perfect -- to make a joke of it makes light of it and doesn't put him in an uncomfortable or awkward position.