Named after notorious sex-pervert and nazi party member Reginald Zweigart, a 'messy reggie' is a deviant sex act. The exact nature of the 'messy reggie' is uncertain, however it is believed to be scatalogical in origin. In modern use, the term may be applied to any sex act that one perceives as disgusting or insulting to one's character.
"I don't like to kink shame, but once he asked for a messy reggie, I knew we weren't compatible."