Ῥύγχος ἔχων τοιοῦτον, Ὀλυμπικέ, μήτ᾿ ἐπὶ κρήνην ἔλθῃς, μήτ᾿ ἐνόρα πρός τι διαυγὲς ὕδωρ. καὶ σὺ γάρ, ὡς Νάρκισσος, ἰδὼν τὸ πρόσωπον ἐναργές, τεθνήξῃ, μισῶν σαυτὸν ἕως θανάτου.

Having such a face, Holupikos, neither come upon a fountain nor come to some pure water, like a mirror. For you also, as Narcissus, when you see the form of your face, you will die, hating yourself unto death.

Or, what I think it's driving at with a little smoother English and a little extra interpretation.

You have such a face, Holupikos, don't go either to a fountain or water pure enough to act as a mirror. For you, just like Narcissus, when you look at your face you will die, hating yourself so much that you will kill yourself.

That's not a very nice thing to say!