A "Waxer" is that metrosexual pretty boy who is so into personal grooming that he has his eyebrows waxed. It is used by manly men as an insult toward those metrosexual narcissists who think they are masculine yet get their eyebrows waxed like a lady. It is equivalent to calling someone a "loser" or "hoser". Can also be used to refer to pretty boys who pluck their eyebrows, although they can also be called "Pluckers" which is an equally humiliating insult.
Woman: *perks up* Wow! Look how PRETTY that guy is!
Manly Man: He's a waxer!
Waxer: *noticing others glancing his way, thinks to himself...
"I'm so damn HOT and that manly man over there is probably jealous of his lady eyeballin' my wicked good looks!"*