What should I do about creepy customer at work?

There's a "customer" in a store I work in who won't leave me alone and since I hate confrontations because I'm afraid of what might happen if he gets angry at me so I just try to be polite to him as much as possible but I don't know if I should keep putting up with him following me around the store and asking me out for the 100th time or firmly tell him to leave me the fuck alone and worry about my safety for the rest of my time working there.
What should I do about creepy customer at work?
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