A Roman Party is a party in which a guest pukes and then proceeds to request more food or alcohol. Any party may become a Roman Party, and said party does not necessarily have to have anything to do with a toga party or any other Roman or ancient world theme party. Comes from the ancient tradition of Roman feasts where a "vomit trough" was provided for guests so they could purge themselves and then continue to feast.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.