I'm pretty sure this is common knowledge among Lemmy's politically engaged userbase, but with this community having been closed for eight months, I'll try to nail down a (verbose) definition here:

• A person ("the victim") has been treated cruelly and unjustly.
• The victim directly helped in advancing e.g. a statute, politician, philosophy, or organization ("the leopard(s)") via endorsement, voting, activism, etc.
• The leopards have substantially harmed a group of people through cruel and unjust actions ("eaten their faces"), and there is a logical throughline from the leopards to the face-eating.
• The victim knew or reasonably should have known that the leopards would eat people's faces if given the power to. They helped the leopards anyway because they're indifferent to or actively enjoy this group's suffering.
• The victim is then shocked to find that the leopards have eaten their face as well ("I didn't think the leopards would eat MY face!"). Usually, any reasonable outside observer would have concluded that the victim was likely part of the group whose faces the leopards would eat.
• A common element is a lack of an apology to anyone the leopards have hurt, tacitly indicating they haven't learned any real lesson in empathy and only care that they have now personally had their face eaten.
• Another one is the (incorrect and denialist) belief by the victim that the leopards have simply eaten their face in error and need only be informed of their mistake to make it stop. (E.g. pleading on social media to a politician about their specific case).

A prototypical example:

>Adrian Personson relies on assistance they receive through Social Service. They endorse and vote for the Austerity Party – knowing one of their main promises is to slash spending by making sure Social Service doesn't go to the people who "don't deserve it". The Austerity Party wins against the Social Spending Party and ascends to power. To Adrian's shock, they receive a letter months later stating they've been cut off from Social Service. They take to social media to write an outraged post about how they're a good, honest person who doesn't deserve this.