Real Men Wear Pink/Analysis

This actually works two different ways:

It advertises manliness by saying that behaving in a way perceived as feminine cannot tarnish it
- Related to this was the use seen in Unseen Academicals: the wearer is so manly that he's not afraid of being challenged on the perceived femininity of his appearance.
It suggests (or asserts) that the person is so manly that he causes his behaviors and attire to be masculine, rather than the other way around.