An action or verbal statement that is committed or said around an accomplice which can be referred to as a homosexual-like statement either said or done on purpose or on accident.
Person #1: "Yo bro I looked that guy for one second then he winked at me!"
Person #2: "Not gonna lie chief, that's pretty sus"
That guy: "Hey cuties!"
sus is short for suspicious. someone can be sus if they have been acting shady or fishy about something. sus is just a short way of saying that something feels suspicious about someone or something.