A heretic
A heretic is someone who hates Warhammer 40k so much they make the Imperium look bad. They’re the worst kind of fanboy.
@NotA40kFan: "I hate the Imperium and everything about it."
My friend called me a heretic for not liking the Inquisition.
My brother got excommunicated from the 40k fan club for saying the Adeptus Astartes were overrated.