Laudator Temporis Acti

Aristophanes, Wasps 163 (tr. Alan Sommerstein):

By Poseidon, Philocleon, never.

μὰ τὸν Ποσειδῶ, Φιλοκλέων, οὐδέποτέ γε.

Sommerstein (Warminster, Aris & Phillips Ltd., 1983) ad loc. (pp. 166-167):

[I]n Ar. slaves (with the exception of the domineering Paphlagon in Knights) do not address their owners by name, but they may so address other free men (Ach. 949, 1085) and Philocleon is no longer Xanthias' owner (see on 69 and 87). A century later in Menander we find slaves addressing by name not only their former masters (Sik. 364, 368, 377, 381, 385) but even their actual masters (Dysk. 247; Sam. 192; Sik. 135, 142) without any hint that this is presumptuous.

Cf. Servius on Vergil's Aeneid 12.652:

For it is an insult to address a superior by his name.

nam contumelia est nomine suo superiorem vocare.

According to the critical apparatus of Douglas M. MacDowell's edition of Aristophanes' Wasps (Oxford: Clarendon Press, 1971), the attribution of line 163 to the slave Xanthias is actually a conjecture by Beer.

MacDowell in his commentary on line 143 (ἄναξ Πόσειδον), p. 150, has an interesting comment on addresses to gods in Aristophanes:

When ἄναξ or ὦ ᾽ναξ precedes a god's name in an exclamation, it marks surprise or annoyance at a sight or event which is unwelcome or unpleasant; cf. Akh. 84, Peace 180, 238, Birds 277, 295, Lys. 296, Wealth 438 (all of which have Ἄπολλον or Ἡράκλεις; there are no other instances in Ar. of ἄναξ Πόσειδον as an exclamation). When Poseidon is invoked in admiration, ἄναξ is always omitted; cf. ὦ Πόσειδον in Knights 144, Peace 564, Frogs 491, 1430.

For more on ancient forms of address, see here.