In the first game, there's a level in which the titular character is on a date with the girl of his dreams and suddenly feels the call of nature. Rather than using the facilities at the park he's at, he tries to hold it in for as long as possible, even while driving. Sunny apparently has a scat fetish, because she seems to be really turned on by it. That's right, a scat fetish, in a K-A rated game. And then when PaRappa goes back to the car after taking a dump, Sunny thinks to herself, "He's the same PaRappa again. Oh well." Apparently she likes him better when he's holding in his feces.
Not to mention the fact that her petals start moving in a very...peculiar manner...
Even better than that: if you complete the first PaRappa game you can go into the title screen menu and choose level select. This allows you to get massive amounts of bonus points for changing the rhythm of the call-and-response lines from the teacher. If you do well enough the meter reads "U rappin' COOL!" and the teacher disappears, allowing you to freestyle with several phrases used in the level. If you get creative on level four (the cooking level) you can actually make PaRappa say "See foo', all we gotta do is M.I.X. the crack, put the cake in the crack, budda-budda-crack, budda-budda-crack" and so forth.
In the second game, Chop Chop Master Onion has a show that's "Strictly for Adults" and Parappa and his best friend try using the moves on each other while unbeknownst to the two of them, Parappa's father and girlfriend's father watch. This is never mentioned again. This time, it's only one-eighth of an E-rated game, but lyrics include "Caress your lover" and "Let's get it on." Very subtle, Sony. Very subtle indeed.