When a women or zombie begins to rot in the genital regions. This could also stand for the male rectum in a similar situation.
Vaginal Decay can also stand for when an incident so horrible occurs it frustrates someone beyond comprehension so strongly that their vagina and/or anal region deteriorates or decays while still living. (or feels as though it has.)
A women with a immensely foul vagina or a man's fungus ridden unwashed anus.
The worse part of the zombie invasion was the putrid stench of vaginal decay.
That math test last week was so intensely frustrating that I felt as though I would be consumed by vaginal decay.
That girl in my science class wreaks of vaginal decay, she probably hasn't showered in decades.