If Dick takes a seat in a nearly empty movie theater (train, plane, or bus) and someone chooses the seat next to him several things could happen. The stranger can be obnoxious enough that Dick moves, he can accept the situation, or Dick could become so obnoxious he forces the other person to move. If Dick needs information from this stranger, or if the stranger is targeting Dick, you have conflict.
If Dick is lunching alone and Jane, a stranger, takes the seat across from him, she is either crazed, wants something, or has mistaken him for someone else. Either way you can have fun with it. Characters don't share tables or hotel rooms with strangers unless there is a very good reason for it.
If someone at work consistently encroaches on Sally’s personal space (or work responsibilities), Sally might dread going to work. She may ask to switch offices or even quit. She might take an aggressive approach and escalate the territory war until the other person gives in or quits. This can serve as a scene obstacle or a personal dilemma.
If Dick is an interrogator, he may encroach on a suspect or witness's personal space to intimidate them. Intruding into someone's personal "bubble" is an act of aggression. It could also be an act of intimacy. Who do you really want to have up close and personal? Whose touch is acceptable?
If a sibling encroaches on Jane’s side of the room, she might complain to mom and dad. If that doesn’t work, it can escalate into petty acts of retaliation until one or the other wins, they agree to a truce, or mom and dad step in and separate them. These kinds of disputes can happen between teachers at school, soccer moms on the field, or waiters at a restaurant.
There are many reasons why one person's "bubble" is wider than anothers based on their past history, trauma, or training. You can use it to define character.