Basically a synonym for the word slut. based on the pokemon ditto, who is known to be capable of breeding with almost any other pokemon, to call someone a ditto means they will have sex with anyone.
guy 1: That girl is so hot, I'm gonna go ask her out
guy 2: Careful dude, she's a ditto, you never knowwhat kind of disease you'll get
Great name for a pet, when you've adopted, for instance, your second Laborador Retriever after your first Lab passes away. A nice way to honor your previous pet! Name for successive pets of the same breed.