The Shampoodle is a location in the Animal Crossing series starting with Animal Crossing: Wild World on the Nintendo DS. It would later appear on the Wii video game Animal Crossing: City Folk. In both games, Shampoodle is owned by a dog named Harriet. Shampoodle is basically a barber shop.
In Animal Crossing: Wild World, the Shampoodle would appear in Tom Nook's final expansion of his shop called Nookingtons in the second floor. Harriet would ask a variety of questions about yourself which would ultimately determine what type of hair and hair color she'll give you.
In City Folk, Shampoodle is available from the start in the city. The same conditions above apply here as well as to what type of haircut you can get, though this time around you can also purchase masks of your Miis here too and wear them. In both versions, if you go there often enough, Harriet will eventually suggest that you get the opposite gender's hairstyles. The questions have the same concept.