A nude character is featureless except for their naughty bits.
A mascot based on a species with no external genitals is drawn with them.
Inanimate objects have genitals in the setting.
A character seems to lack detail in the private areas, but it's just skin-colored patches.
Alternatively, as more commonly used in the Furry Fandom, the important parts are obscured by fur.
The character is in "cyberspace" or some other form of out of body experience, the lack of details could even be a subconscious desire for modesty or enforced to avoid problems.
The character is in the middle of the fog.
The character is an android and doesn't need genitals, so they don't have them.
Or, as in some hentai, the parts in question aren't visible, but are very clearly demonstrated to be present and in working condition.
...but when the patches are removed, nothing's underneath.'
When shaved, the furries still have nothing.
The character really does lack genitals.
The character steps out of the fog, and is revealed to have no genitals.
Real humans in the setting also lack genitals.
Parodied: The areas in question are rendered so as to look plastic, like on a Barbie.
Zig Zagged: In one scene, the character is drawn with no detail, while in the following scene Fan Disservice-y levels of detail are shown, then the character is drawn with no detail again, and then a normal level of detail in the fourth scene.
Played For Laughs: Everyone reacts as if there actually is genitalia down there, be they reactions of sexual attraction to the nude person or reactions of horror at the trauma of seeing their naughty bits.