The theory that states that one judges a guy/girl's hottness by comparing him/her to those around them. This explains why one would think someone is hotter when seen at, say a movie theater, than at school. There are fewer to compare them to.
Guy 1: Dude, that girl that goes to your school is really hot.
Guy 2: Naw, that's the theory of relative hottness. At school she's not that hot.
The phrase will only be understood by dirty minded people. A word that starts with p and ends with orn is guessed to be porn as it IS the hottest part of the movie industry however the real word is popcorn! Used as a trick to see if someone is dirty minded.
"Hey frank, what starts with P and ends with ORN and is the hottest part of the movieindustry?"