He avoided answering questions about what he was doing last night; it was so sus.

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The term “sus,” which is short for “suspicious” or “suspect,” can be traced back to the 1920s. It was initially used in criminal slang to describe someone who was suspected of being involved in illegal activities. In modern times, "sus" saw a significant resurgence in popularity with the rise of the game "Among Us," which was developed by InnerSloth and released in 2018. The game gained widespread popularity during the COVID-19 pandemic in 2020, becoming a cultural phenomenon.

In "Among Us," players are assigned the roles of either crewmates or impostors. Crewmates work together to complete tasks around the map, while impostors aim to sabotage their efforts and eliminate them without being caught. During discussions and meetings, players use the term "sus" to accuse others of being the impostor based on their behavior and actions. “Sus” quickly began to spread from the gaming community onto memes and popular social media platforms.

It is now used in slang to describe strange or suspicious behavior, typically with a humorous anecdote. For example, one may poke fun at their friend by calling them “sus” because they choose to use private rather than regular internet browsing.