How did Brinker Hadley pose a threat to Gene?

Brinker's nature certainly seems more questionable in this chapter than it was after his introduction. Seeing Finny is back, he immediately brings up Gene's "little plot" to keep a room to himself by hurting Finny; it is hardly a tactful thing to say, and is taking the joke of the day before much too far. That Brinker is willing to bring the whole subject up again, in front of both of them, means that he believes there is some truth in the matter. But why Brinker would think that Gene was guilty of harming Finny, when he wasn't present when the accident happened and no one else thinks badly of Gene, is quite a mystery. Perhaps Brinker is meant to be some kind of conscience figure, with his goading of Gene and determination to enlist.