Where a burger is purchased from a burger establishment (burger king, MacDonald's) Then at their property the man lifts the bun of the burger off and dumps his load on it, then he must suck period blood from the woman's vagina and spit it on the sauce. The woman then must mix the sauce up with her tongue replace the bun and eat it with the man. This is similar to a rainbow kiss on a burger.
Eddy: Me and craig took our relationship to the next level!
Paddy: I really dont want to know your dirtyer than urban dictionary
Eddy: Shut up. We put some rainbow sauce on a burger and ate it, it tasted divine.