Rabbanian's Law of Confusion
Started out as a theory, but over the years has developed into a law: If you can't tell, it's always a man.
The bros were walking through the gay parade on Halloween and were overwhelmed by all the tits, when one of them remembered Rabbanian's Law of Confusion. They were all on high alert and realized any pair of those juicy titties could easily be accompanied by a set of dick and balls down low.