How do you set boundaries when you want a guy to stop talking to you?

How do you end a conversation and inform him that he being inappropriate?

How do you tell a guy he makes you uncomfortable?

Basically there this creepy guy who comes and talks to me face to face and i tried being nice and i tried the typical signs like not responding when he talks to me, walking away, pretend I’m busy, have a friend near by to come in and save me. My supervisor said i need to be more firm and set boundaries. I’m having troubles bc this guy makes me uncomfortable and creeps me out….

I normally know how to set boundaries but this situation hard because I’m creeped out by this man…