Oysters make you horny?!
Oysters are rich in zinc, which is needed by the body to make testosterone. However, this in itself doesn't make the body want to make testosterone.
Oysters contain a lot of zinc. Zinc deficiency impairs the functioning of the sexual organs and reduces the production of sex hormones (hypogonadism). A hefty dose of zinc is likely to enhance the sexual desire and functioning of a hypogonadic person. However, a similar dose given to an eugonadic person is not going to make that person feel ever more sexy, just as eating more and more protein will not magically cause the muscles to grow ever larger. There's always a ceiling somewhere.
Additionally, oysters and other forms of seafood do not remain fresh for very long. Most seafood items purchased from a supermarket are likely to have gone rancid to a certain extent, a process that involves oxidative damage to the lipids and other entities in the food (lipoperoxidation). Lipoperoxidation inhibits the functioning of the sexual organs, and so it is possible that some rancid oysters could temporarily make a person feel less horny.
So they claim.... but it has never worked for me either.