Most Helpful Guy
Yes they can indeed avoid a girl/guy they have feelings for like the plague, it depends on their view of a possible outcome of being with the person they like.
It has happened to me before and one more than one occasion. I have liked a girl and never believed I could be with her (I never even asked her out and already was admitting defeat) and therefore I kept my distance and believed that by avoiding her I could get over her and well that never worked too well because when I then bumped into her our interactions were awkward and those feelings came flooding back haha.
Most Helpful Girl
No, not generally, that would be weird.. if they liked someone, they would try to spend more time around that person.