What would happen if u used expired shampoo that smelled really bad and it got on the vagina , would i devolep an infection down there?

Interesting but unclear question. Shampoo is usually a thick liquid to help wash hair. It is often scented but may be unscented, but whether one thinks the scent is great, so-so, or really bad, should not alter the function of the shampoo (unless maybe it's super old, years past expiration date, and stored in a harsh environment). Most importantly, the VAGINA is inside the body and grows no hair.