Imagine a pureblood is taunting a muggleborn and being a general dickbag. The muggleborn looks them dead in the eyes and says "at least I'm not being Prince Joeffry," and walks away.
The pureblood will be confused.
Any muggleborns witnessing the fight will be oohing and laughing at said pureblood.
Because we all know Joeffry is the physical incarnation of period cramps.