I rejected my colleague 6+ months ago but he's still pursuing me. How do I make it clear he makes me uncomfortable?

I rejected my colleague as I'm not interested and have a boyfriend and I made this clear when I said no.

However he still messages me, asks me to hang out, and seems to laugh at everything I say even when I'm not joking.

It really truly makes me so uncomfortable. I try to avoid him outside of work but I'm wondering what else I can do while keeping it amicable and professional.

Not sure if this changes anything but I manage him and he's slightly older than me.

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I've done about as much ignoring as I can do, honestly to the point of being rude. E. g. he comes up to my desk and stands next to me until I acknowledge him. The longest I ignored him for was about half a minute or so.

My boss actually knows about the situation too but can't do anything as he's not actually doing anything wrong.
I rejected my colleague 6+ months ago but he's still pursuing me. How do I make it clear he makes me uncomfortable?
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