There's a yokai whose face are buttcheeks.
There is mild sexual innuendo (along the lines of Rocko's Modern Life) in the uncut Japanese version, some of which has been censored from international versions of the show.
In one episode, a group of boys stay up late to watch a show meant for adults only. We see girls in bikinis on-screen (in the Japanese version, they're two-piece; in the English dub, they're one-piece). The show is also referred to as the "ample boing hour" only in the Japanese version.
Another episode has a gag involving a robot enjoying getting a blade in his rear end. This scene is slightly edited in the English dub to make the innuendo less obvious.
One character, Manjimutt, acts quite flirtatious towards women (which makes sense since he used to be a human man); in one episode, he gets a job as a photographer, only to be fired when he takes photos focusing on the woman's chest. This is left in the American version.
At least one Yo-Kai, Insomni, is depicted with a female humanoid form and wears low-cut clothing. Teenage boy characters in the series are also shown to be interested in inappropriate films, though nothing is shown, and occasionally fawning over idealized female characters.