Tell someone to chill

Man lai：
To tell someone to chill out means to tell someone to keep calm , to be at ease.

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chill or chill out means to "stop" or "cool down" from being excited or serious about something.

You also need to know the context, above is when you're very angry/serious about something/someone and the other person say this means he/she is bother/upset by you.

If in a generally peaceful conservation/situation, somebody say this only means "don't be so serious" or "take it easy". Not really upset by you.

Since this is conversational language, this is just some possible meanings.