Why did Fry call himself Cosmic F?

[on:]

In the flashback scene in "Luck of the Fryish" where Fry and Yancy were break dancing Fry said his nickname was 'Cosmic F'. 

The question is, his name is Phillip.  So, why didn't he call himself "Cosmic P" instead?  Yancy called himself "Cosmic Y", so why did Fry use the first letter of his last name?  He should've called himself "Cosmic P" unless of course he was scared of being the butt of urine jokes perhaps.

[Reply #1 on:]

Probably because that's what everyone calls him. Fry is what he goes by in the furture and his past.