To take advantage of a woman that normally finds you extremely unattractive, usually done when the girl is either emotionally distressed or extremely intoxicated
Bro 1: Where did audrey go? She passed out on the couch a few minutes ago
Bro 2: I think william took her upstairs....
Bro 1: There he goes again, always pulling a robbie
On December 14th, you go to a person who has been given the nickname "Robbie" and try to win him over for the day. It becomes bonus points if he is in a current relationship
"Hey, have you seduced a Robbie yet? Its still National Seduce A Robbie Day"