It’s part of a hazing ritual that actually happens before the wedding. The bride is taken by surprise, by hands down the crummiest friends you could have, and covered from head to toe with foul substances such as eggs, various sauces, feathers, and, well, you name it.
The ritual of covering brides and grooms in treacle, soot and flour used to be carried out to ward off evil spirits. It still happens in parts of Scotland.