Considering that series is based on classical mythology ...
Much of Percy's interpreting for Arion consists of this.
In "The Lost Hero", it mentions that Drew dumped, "everything from the bathroom waste bin- some pretty nasty things- all over the floor".
Also, Piper's father says that he thinks "That Indian and Greek stuff is all bull "
In The Son of Neptune, the Amazon, Kinzie, blatantly flirts with Percy, telling him if he ever needs a new girlfriend, she's available. While we're never told exactly how old Kinzie is, it's safe to assume she's an adult (since not many teenagers can get jobs as security guards), whereas Percy is only sixteen. Plus, you have to wonder what Kinzie was thinking when she says Percy would look great in an iron collar and an orange jumpsuit.
In the same vein as Percy and Kinzie, The House of Hades also gives us Leo and Calypso. There was also a part like this back in the first series, though with Percy instead of Leo. Keep in mind that, again, Percy and Leo are only about 16, whereas Calypso is over 3000 years old.
From The Mark of Athena we have one scene where Percy and Annabeth fall asleep together on the ship. With some of the dialogue, one has to wonder if the original scene was a Sexy Discretion Shot so that Riordan could get it past the radar.note To make things even more scandalous, Leo is just grinning and shaking his head in a way that screams Did You Just Have Sex?, and Hazel is scandalized, because she was from the 1940s.
Annabeth: We just fell asleep together! We didn't do anything.
Percy: We kissed a few times...
Annabeth: Not helping!
Percy referring to Ephialtes as "The Big F."
There is a scene in The Son of Neptune where Hazel takes Percy to the back of R.O.F.L. to help him get better and to call Camp Jupiter, while Frank goes outside to fight some monsters. Later, we find out that Percy and Hazel used an Iris Message to call Reyna...who at the time was taking a bath...did I mention that Iris Messages are basically video chat? Frank also says he would have paid to see that (meaning he would have liked to see Reyna's shocked look, not her in the bath...or would he?)