Stobaeus 3.38.32 = Hippias, fragment 16 Diels-Kranz = Plutarch, fragment 155 Sandbach (tr. David Gallop):
From Plutarch's <On> Slander: "Hippias says that there are two kinds of envy: one kind is just, when one begrudges bad men the honor given them; the other kind is unjust, when one begrudges it to good men. The envious have double the distress of others; for they are vexed not only, as others are, by their own ills but also by others' goods."
Πλουτάρχου ἐκ τοῦ <περὶ τοῦ> διαβάλλειν·
Ἱππίας λέγει δύο εἶναι φθόνους· τὸν μὲν δίκαιον, ὅταν τις τοῖς κακοῖς φθονῇ τιμωμένοις· τὸν δ᾿ ἄδικον, ὅταν τοῖς ἀγαθοῖς. καὶ διπλᾶ τῶν ἄλλων οἱ φθονεροὶ κακοῦνται· οὐ γὰρ μόνον τοῖς ἰδίοις κακοῖς ἄχθονται, ὥσπερ ἐκεῖνοι, ἀλλὰ καὶ τοῖς ἀλλοτρίοις ἀγαθοῖς.
περὶ τοῦ add. Otto Hense
One could look at it another way. The envious have double the joy of others; for they rejoice not only in their own goods, but also in others' misfortunes. See Plato, Philebus
But certainly we see the envious man rejoicing in the misfortunes of his neighbours.
ἀλλὰ μὴν ὁ φθονῶν γε ἐπὶ κακοῖς τοῖς τῶν πέλας ἡδόμενος ἀναφανήσεται.