I completely understand why you're worried about this, having had a similar problem in the past. There are one or two people I have worked with in the past that I would prefer not to be near again, and like you I work in a particular sector where people tend to know each other.
It's essential to have choices when dealing with conflict and challenge, and while avoidance can be an option, you cannot allow this to determine your life! The person sounds remarkably stupid and immature and so all the more reason that you cannot let them have power over you.
Don't attempt to follow their movements on social media, don't have social contact with them in any way. If you find them in another workplace, deal with it differently next time- distance yourself from them, any sign of bullying you report immediately to the supervisor/manager as it's their job to deal with this stupid and destructive behaviour.
Your best revenge is to be successful, so don't waste your time watching them, use the energy instead to focus on your ambitions.
Best wishes xx