Invoked humorously in Nobilis 3rd edition. Lord Entropy is a cruel tyrant who has outlawed love for Nobles. Even so, some observers were surprised that no one seems to have fallen in love with him, despite him being a "deeply troubled, handsome, dangerous celebrity." Experiments seem to prove that it's impossible to love him, and it's likely that he's either responsible for the phenomena or glad that it exists.
A really understated example is Imperial Commissars. Due to the popularity of characters like Ibram Gaunt and Ciaphas Cain, the average Commissar is often thought of in the fandom as A Father to His Men, maybe a Jerk with a Heart of Goldat the absolute worst. What people forget is that Gaunt and Cain are the exception, not the rule. The average Commissar will execute Guardsmen over trivial offences and gladly send them to die horribly in pointless assaults and Last Stands, a practice which disgusts the alien Tau.
This could apply to a lot of the "good guy" factions in Warhammer 40000, to be honest. And Games Workshop don't take kindly to that. The Imperium looking too justified in their extremism? Next edition, add more deluded Knight Templars screaming "HERESY!". The Eldar looking too sympathetic? Play up their The Fair Folk tendencies by showing them orchestrating events which lead to the deaths of billions of human civilians to save the lives of a handful of Eldar. The Tau looking too hopeful and progressive? Add recently confirmed rumours of mind-control, sterilization and generally treating their auxiliary races like second-class citizens. The Orks looking too much like Plucky Comic Relief? Make a game where Orks are seen laughing gleefully as they massacre women and children. Warhammer 40000 is straight up Evil Versus Evil, maybeBlack and Gray Morality at the best of times, so the moment any faction begins being viewed as "good guys" or at the very least "alright", lore will update showing that faction committing horrible atrocities to remind everyone that no-one should be cheered on in this series.