A woman's genitalia that hasn't been properly cleansed over the course of a week to month. In order to be a blooming onion, this vagina has to have an odor that burns a man, or woman's, eyes as they approach for oral intercourse. When spreading the vaginal lips apart, one must cry from the odor, else the genitalia isn't a proper blooming onion.
Evan was so drunk last night, he licked a prostitute's blooming onion. He woke up this morning with a hangover, a bad taste in his mouth, and crazy red eyes from crying all night long!