This is not true, the Greeks did find humour in the antics of the gods, but they did not turn them into "jokes",
"Laughter was not marginal in the Greek conception of their gods. Considering how it surfaces again and again in the context of myths and ritual, it must rather be seen as a defining characteristic of the divine world...
People laughed at the exalted gods, at the crippled Hephaistos and at the amorous Aphrodite and her fierce lover. The gods had laughed first: all of Olympus roared with laughter at Hephaistos’ performance, and at least the males among them showed uninhibited delight at the torments of the lovers and the agony of the cuckold.
Human laughter was mixed with that of the divine, demonstrating that it was permissible to laugh at the gods." (emphases added)
Gilhus, I. S. (1997).
Laughing Gods, weeping virgins: Laughter in the history of religion. Routledge.
"For a different laughterless ritual..see Paus. 9.39.13...
At the opposite extreme, some Greeks had no qualms about mocking religious practices themselves." (emphasis added)
Halliwell, S. (2008).
Greek laughter: A study of cultural psychology from Homer to Early Christianity. Cambridge: Cambridge University Press.
"the Eleusinian Mysteries in classical Athens made provision for multiple ‘official’ moments of ritualised scurrility and associated these with Demeter’s own delight at being (sexually) mocked by an old slave woman (Iambe)"
(ibid)
"Sexual adventures on the part of male gods can certainly be regarded on occasion in a comic light:
Zeus’s many adulterous affairs receive this treatment in, for example, the mythological burlesques of Attic Middle and New Comedy" (ibid)
Even when certain Greeks were explicit about not mocking the gods, they testify to the fact that other Greeks did:
"A drunken Bacchus, like a philandering Zeus, a spiteful Hera, or a cheating Apollo, might be acceptable to an heroic age, or even in the fifth century, when people could make fun of their gods without losing respect for them; but it was not so easy for people to take this attitude since the days of Socrates. So Philochorus wrote: 'We must not regard Dionysus, as some people represent him, as a kind of clown and buffoon'"
in fact the reverse was true; they considered themselves as the playthings of the gods.
"Although the gods are portrayed as capable of laughing in several ways, from the affectionate to the bitterly caustic, from the conciliatory to the triumphalist, why is it that they never laugh at human beings (never, for sure, at the human condition), only at themselves"
Gilhus, I. S. (1997).
Laughing Gods, weeping virgins: Laughter in the history of religion. Routledge.