Mark Hoppus confirmed on his Tumblr that “Josie” was written with “an imaginary ideal girlfriend” in mind. When looking for a name, his friend—Elyse Rogers from Dance Hall Crashers, a band mentioned in this song—suggested Josie, the name of her dog.

While “Josie” was the fourth single off of Dude Ranch, it was the second most successful after the classic “Dammit.” The song’s humorous music video features actress Alyssa Milano as the girl he pines for, presumably Josie, and follows Mark’s derailed attempts to win her over.
https://www.youtube.com/watch?v=I6kfin-UeAQ