You've heard of Golden Shower
s. You've may have even heard of Brown Shower
s. You'll want to jump in the shower after reading this. Just don't read this if you're eating.
Bluntly put, a person who is into Roman Showers is one who enjoys other people vomiting on them, smearing the vomit all over, perhaps even ingesting it, or vomiting on somebody. It's more common to find people that want to be on the receiving end than it is to find someone to be the donor.
This fetish poses serious health risks because of the toxins contained in vomit. Even if you're just vomiting on yourself, doing it semi-regularly has a tremendous impact on your internal organs. There is ample information on the health risks of vomiting on the bulimia node, so I won't repeat it here.
The phrase was coined as a reference to the early Roman Empire, where vomiting inbetween courses was the shared, common method of surviving multiple-course meals.