The idiom "the devil is beating his wife and marrying his daughter" is mentioned. A medieval man announces his intent to 'breed' with his sister. Nothing is shown onscreen.
The old idiom 'the devil is beating his wife' (used to describe a sunshower) is commented on; Lucifer hears of it and is offended by the implication. No domestic abuse occurs on screen or otherwise.
At one point, a little girl says that her father used the term 'queers' derogatorily. While this term is reclaimed by many in the LGBT+ community and is commonly used simply to refer to people who are not cisgender and/or heterosexual in general, this is worth noting. Also worth noting that the old homophobic trope that gay people go to Hell is used prominently, but it is explained as moreso about God wanting Lucifer to find a partner and be happy rather than anything being wrong with being gay. As always, though, avoid the comments.
One strip implies that a woman who went to Hell used human meat in her cooking. A pair of talking dodos are eaten by humans, although YMMV on the latter.