In CAS give your Sim the Painfully Shy trait. Conflicts with Outgoing trait, Party Animal Trait, and Insider Trait.
This trait unlocks new social interactions and menu.
Using the Sorry I don’t like to talk much interaction will give your Sim the Socially Invisible buff that will make them feel uncomfortable.
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When they use the It’s hard for me to open up interaction they’ll get the Quiet buff that’ll make them feel embarrassed.
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When they are with a sim they don’t know very well, they’ll get very uncomfortable from the Painfully Shy buff.
