How and why did John upset the floorwalker in the store in The Pigman?
I am assuming that you are asking about the floorwalker that John, Lorraine, and Mr. Pignati encounter at the pet shop. The three of them are looking at some monkeys in a cage, when John suggests that they should give the cute creatures a piece of their popcorn. Lorraine offers her can of "Love'n Nuts" to Mr. Pignati so that he can give them to the monkeys, but the "nasty floorwalker" sees them and calls out, "Don't feed them." Mr. Pignati, embarrassed, apologizes immediately, but John, who is not one to take orders automatically from anyone, asks, "Why not?" The floorwalker rudely replies, "Because I told you not to, that's why," which is the worst thing he could have said to John, who has an extremely rebellious nature. Lorraine thinks that had the floorwalker simply given John a reason for his command, such as that monkeys bite or that popcorn is not good for them, John would have had no problem following his directions. Since the employee's attitude is so confrontational, however, John's natural reaction is to defy him, so
"every time the floorwalker half turned his back John (makes) believe he (is) throwing popcorn into the monkey cage,"
and Lorraine thinks that the frustrated man is "going to go insane" (Chapter 8).