"The List" is a compilation of all the hot guys in a specific group (your school, band, etc), with #1 being the hottest.
Rules of the list are determined by the list makers.
When you have sex with someone that you have had sex with in the past -- But it only counts if you have slept with someone after you go back on the list because then it wouldn't really be going back on the the list now would it.
Sleeping with an ex-girl friend after you have slept with someone else.
De-friending a person, or lowering them in one's social hierarchy, based on a perceived infraction of the terms of your relationship. Also abbreviated as "OTL."