Brinker believes it's important to mention Finny's leg to him and even make jokes about it. Why?

When Brinker makes a remark about Finny being crippled and sidelined, Finny just accepts the remark, rather than giving Brinker heck for saying such a thing. Brinker's behavior turns vindictive and strange in this chapter; where his extended joke about Gene's guilt was a bit odd, his obsession with Finny's accident and condition is odd. Is Brinker just a standard flat antagonist figure or is their something more to his hatred of Gene and Finney. Perhaps Brinker is jealous of the bond these boys have or perhaps there is more going on. In any case Brinker serves as an antagonist that reminds the boys of the unspoken tension they are trying to forget.