Rejoicing at or deriving pleasure from the misfortunes of others.
That feeling of misplaced glee you feel at someone else’s misfortune.
Epicaricacy is mentioned in some early dictionaries, but there is little or no evidence of actual usage until it was picked up by various "interesting word" websites around the turn of the twenty-first century.
From Ancient Greek ἐπιχαιρεκακία: "joy upon evil."