How can I be more assertive at work?

The managers son , who Is 20, has started my place of work. However, he's started talking down to me and belittling me but in a covert way. So it's not something I can report or I'd seem paranoid and foolish. I have no idea how to deal with the situation with him being the managers son.

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10 mo
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How can I be more assertive at work?
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