Casually ignore them and walk away.

Then I'm not in sight anymore I circle back around and follow them to their car, noting their plate number to I can pay a police buddy to get me an address. The I follow them to until I know where they work and what their job is.

Then I take on training and job experience that would make me a good manager for that type of work, and monitor job postings at their company until I see my opening, nail the interview, and become their boss.

At this point, they've likely moved on and forgotten who I am.

But I haven't forgotten them.

I proceed to make their job miserable and impossible, until one day I call them into my office to explain that why need to let them go for poor performance. Then I lean way in, right up in their face, and say quietly "And, to be honest... I don't like you."

Then I quit and go back to my normal life. No sweat off my back.