Have these people been bothering you or are you collecting pieces from what have happened in the past, and planning out scenarios?
When doing that, you've got to be careful because your mind tends to pick "Worst-Case Scenarios". You've got to think of the realism involved in that... Let me elaborate.
You, for example, see this person(s) as a threat. A threat to you physically, emotionally and/or mentally. Instantly you are nerve-racked about what they might do have you encounter them in a dark alley. You have pepper spray and you are held back on when is the appropriate time to pepper spray someone. That is also a threat.
If you view it from their perspective, however.... They might not even think two thoughts about you let alone what has happened in the past. You stated you only met one of them. Boiled down to nuts and bolts.... They don't know you. They don't know what you're capable of, what you're capable of doing.... and to them... That is a threat. Doesn't mean that threat is floating above your head every time you're in the same locations... but if they meditated to physically harm you just that alone poses some pretty strong force as to not carry out harm.
That's not even accounting for the fact of social threat. How would something like this go unnoticed? Surely if they were to confront you... physically harm you in any way.. They are looking at some serious repercussions. People don't let that go easily because they don't want the same thing to happen to them. They want to neutralize the threat.
That being said... The first paragraph states that you as a person and what you're capable of is a threat. So out of nowhere are they going to swoop from grappling hooks and physically harm you on your way to the bathroom? There are just too many variables on that. Think of what you'd do. Why doesn't a criminal who steals wheels off of a car steal wheels off of every car in every neighborhood in their entire city? There's too many variables in that. If you continue to stand your ground, Don't let your mind take over what isn't really there, They are not going to bother you.
I wouldn't go into a bar and start swinging on some random guy I didn't first have any knowledge or understanding of what he's capable of. He could be a cold blooded hitman for all I know.
If you pose yourself as healthy and not cowering while they are in your presence there is nothing that they will do to you without you egging it on. You're more likely over thinking the entire situation... as I see you are worried about them coming to your campus next year. I was and still am at times... the same exact way. Think about it like this... They come to your campus next year. So what? Let them go there. If they give you problems don't show your weak side and there is nothing that they will step out of their safezone to do. It's just not worth it.
As for the pepper spray. Keep it handy and make sure you know how to use it. Under stress you're fumbling around you don't know what you're doing... Do your best to keep it in a comfortable spot, that you know the fastest way to activate the spray. If you got it stowed away and it takes you 15 seconds to pull it out, undo the safety mechanism on it and spray your target... that's too much time to waste in a critical situation.
Don't think about using the spray. It's not a talisman and don't rely on it to keep you in the comfort zone. It's a tool.
It is justified to be used when you feel there is a critical threat to your own personal safety or a loved one. It doesn't matter where it is. If you feel that something is about to escalate, remember where it is. If things escalate and there is nothing physically you can do to remove yourself from harm, use the spray. Believe me you know when... if you practice what I said earlier you won't have to think about "Hmm should I pull this spray out now or wait a few minutes". You're going to sense it.
It all just depends on the situation too..
I mean if you pull the spray out and they see that... Nobody wants to take that stuff to the face. I wouldn't even do it if I was drunk.
Tased.... Maybe. I kinda wanna get tased.