PG stands for "parental guidance." It's something that usually accompanies a movie or television series in which could contain certain sexual themes, alcohol/drug use, violence etc. It just means that children should be accompanied by an adult should they wish to watch the show.
If you keep replaying Nina's voice when she says "Nice" , it sounds weird like it doesn't fit her.. haha. That was cute, and Hot when Ian "licked" Kat's face.