There is a overly provocative waitress at the Diner in the move. Nothing bad just flirtation.

A female alien character is featured in several scenes with no clothing, though the only real features in this form are facial.

A character implies anal probing when describing his alleged abduction by aliens. This is seen from outside, so nothing is actually heard. Only adults would understand.

Fred smells the inside of Shaggy's water bottle in one scene. Presumably, Fred was seeing if Shaggy was sneaking liquor. Only adults would understand.

Alien invaders can appear menacing

The "Aliens Are Here" song can be scary, as the vocal distortion sounded evil in the middle of it, despite that the lyrics are mild.