Meaning:
Lit: “to take off/pull one’s panties through the head”. This describes a state of extreme hornyness in which an individual is ready to engage in sexual activities right away, usually in reaction to seeing a very attractive male or female. It is mainly used aimed at women, but nothing in the expression’s meaning excludes aiming it at men. A subset of its meaning stresses a naivety/goofiness of the target, so it’s very often used describing teenage persons, fans of a popular music band of simply, young girls having a crush on a school football star.