Because the world we live in has shifted to be more like the one depicted in Brave New World, we tend to miss some of what would have been laugh-out-loud humor in the late 1920s and early 1930s.
For example, our world relies on a high level of consumption—a level that seems perfectly normal to us, as it does the citizens of the World State. However, England in the 1930s would have had far fewer consumer goods. It would have seemed absurd to people, even in the upper classes, not, for instance, to mend their clothing. Clothing was too expensive to throw or give away because of a rip or a tear. Therefore, they would have found over-the-top, nonsensical comedy in the idea of being conditioned to think that
Ending is better than mending. The more stitches the less riches. . . .
It would be like, in our culture, recommending abandoning a car and buying a new one over a flat tire.
Second, sexual mores were much stricter in the 1920s and 1930s than today. We would probably—at least in dominant society, and not in a religious subgroup—experience little shock over Lenina's conditioning to have multiple sex partners. However, that idea was more startling years ago, and Huxley is, to some extent, mocking the "cutting edge" sexual practices of Bohemian groups like Bloomsbury, a collection of writers and artists who did not behave monogamously. The average reader then would have found Lenina's confusion over John's rejection of her as a strumpet humorous, because, of course, a decent woman would not throw herself sexually at a man. Likewise, John's anguish over dishonoring Lenina because of his sexual desire for her is comic given the sexual ethics of the World State. In sum, their different sexual mores lead to comic misfires.
Further, Huxley mocks Lenina's debased idea of "poetry" when she tries to seduce John, the Shakespeare lover, by quoting the inane line, "Hug me until you drug me, honey." While John exalts her as a goddess, she shows herself to be a shallow fool.
Finally, Huxley mocks industrial society and its worship of the efficiency of uniformity in his depiction of the groups of up to 96 identical twins, which so horrify John.