"Pompous Pep,"
otherwise known as "Endangered Species," is a
euphemism for the Vlad/Danny slash ships in the Danny Phantom fandom. Most ships have code names of this sort (Skulker/Danny is Callous Quarry; Walker/Danny is Jail Bait; Clockwork/Dan is Meddling Minutes) so as to make searching for stories with that pairing easier for fans.
For example, a
lot of stories might have the words "Vlad" and "Danny" in the
description, but more often than not those are father/son fics. Likewise, Skulker is always chasing Danny, and Dan is hardly ever seen without Clockwork right behind him. This is just a simple mechanism the fans created to simplify searching for their favorite pairings, though most fans would like to viciously strangle whoever came up with the sometimes less-than-appealing names.