Why would we be unpolite (impolite) if we told someone to 'zip it'? What do fed up and go on mean?

We use two phrasal verbs in this short video. To be fed up and to go on (and on and on).
To be fed up means to be annoyed, unhappy, or bored with a situation that has existed for a long time.
Some people never stop talking like he does in this video and go on and on means exactly that.
The expression zip it is not very polite but we imagine that we close a zip over the mouth so that it is closed and cannot be opened.

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