If you can see my mustache, you are too close.
As a very new member, where only I can tell with a magnifying mirror, to the "Women with Musrashes Club" - I am certain of one fact...
If you can see a woman's mustache without invading her personal space, she has made a definite decision about her personal appearance. Her decision is rooted in such confidence that you need not say anything about that mustache. Actually, it would be in your best interest and humanity's if you said nothing.
On the other hand, if you see my mustache and you are not my husband, you are too close.