I think he's DEFINATELY an ESFP overall though. No, not because he's stupid (thought he's actually shown to be pretty smart in some areas like most Malcom in The Middle are). Also, both Ti and Fi users can be mainly driven by self-gratification, but just approached differently.
But I think people may type him as an T type because he's mainly mean and violent, which fits a stereotype about T-types.
T types can be nice, they can be dumb. F types can be pretty sharp, they can also be REALLY mean.
Reese is mean, but why? It seems that he's being subjected to the bully stereotype and may feel that that's his identity and the only way he's validated as a person. He mainly feels oppressed and his violence is in response of feeling stepped on by others unfairly rather than a need to be above others because of insecurities. He really only wants to be himself but is afraid that he'll be ridiculed and judged by others.
I think one of the best examples of his Fi showing is when he bought the entire box of caterpillars. He gave them names, was super protective over them and pretty much adopted them, not even once it going through his head how he could use that for practical jokes. He never really had that in his agenda unless it was to get the attention of someone, which is typical of aux Fi.
Another good one is when he befriends and becomes one with a pack of dogs.
When he thought that Malcolm was gay, he bought him a gay-porn tape and actually watched the whole thing because he wanted to know that it was gay enough for him, a great example of how Fi works (a very ridiculous, cartoonish one, but a good one nonetheless).
Fi and Ti can behave similarly. The reasons behind the behavior is usually where we can distinguish them.