The act or reactive measure when the opposite sex makes eye-contact with you and then proceeds to plug in their iPod as a defense mechanism to prevent you from making a move on them.
Josh: I saw this girl on the bus and was going to hit on her, then she busted out her iPod.
When you can't date, or have sex, with someone because they're the friend of someone you dated, or had sex with. Most commonly experienced when one wants to date one of an ex's friends, but they can't, because they're the friend of their ex.