Mr. Vinson is a character that is first introduced to us in Chapter 24, when Holden relates the problems he had with his old school to Mr. Antolini. Mr. Vinson was the Oral Expression teacher, and one of the teachers that Holden struggled with. Note what Holden tells Mr. Antolini about him and his feelings about him:
"You just didn't know this teacher, mr. Vinson. He could drive you crazy sometimes, him and the goddam class. I mean he'd keep telling you to unify and simplify all the time. Some things you just can't do that to. I mean you can't hardly ever simplify and unify something just because somebody wants you to. You didn't know this guy, Mr. Vinson. I mean he was very intelligent and all, but you could tell he didn't have too much brains."
Thus, according to Holden, clearly Mr. Vinson was intelligent, but his intelligence removed him from the practical, down-to-earth world in which Holden lives and operates. Academically, yes, you can "simplify and unify," but in the real, messy world which is of central importance to Holden, it is impossible and ridiculous to have such an attitude. Thus it is that, in Holden's estimation of Mr. Vinson, he is intelligent but lacks brains in terms of how to practically apply that intelligence.