why Little Leroy got upset over arithmatic

In the part where Jerry squares off with Little Leroy in the bathroom, Jerry says, "No lessons in messin', it's gone be reading, writing, an' arithmatic."
Little Leroy blurts out, "ARITHMATIC, M.F.!" etc.

I don't quite get that. Maybe with all the hate L.L. had, he echoed the last word Jerry said with aggressiveness to try to show he was boss?