Get a disguise. It could be as simple as wearing a hood, or as complex as an entire fake identity.
Stay outta’ dodge. Go different routes if you frequently cross paths with them. If you know they are going to be somewhere at a certain time, don’t be there.
Have a predetermined list of excuses. I came up with a few for you.
I’ve been out of town.
I’m on the quest to become a hairless goddess.
I am going to the counselor.
I already have plans.
I was trying to open my third eye.
Pretend to not speak whatever language they’re talking to you in. If you know even a little bit of another language you can probably get away with this trick.
Just move. If steps one through four didn’t help you avoid this person, then your best bet is to simply move away and change your phone number. Some popular options would be France, Siberia, a treehouse in the woods, and Mars.