One of the most iconic images of Oedipus in the 5th century BCE depicts the moment of his interview with the Sphinx. Here is a representative example (Beazley Archive 205372; Gregorian Etruscan Museum, Vatican City, Vat. 16541):
This is the moment when the Sphinx asks Oedipus her famous question. The iconic nature of this also makes it ripe for parody.
This is the best picture I could manage of the scene (if you are interested, see J. Boardman’s article in JHS 90 (1970) 194-195. This vase features the beast masturbating and ejaculating while the hero looks on and holds his sword. It is dated to the mid-fifth century BCE. (I found it in the LIMC, number 69).
There is a much more tame version of the later, which maintains the phallus, but skimps on the erections and ejaculations. This vase is in the Boston MFA, 01.8036.