Dennis isn't a bad kid
I used to think he was a bad kid because he was always getting into trouble and doing bad things. Now as an adult I realize he isn't a bad kid and he is actually sweet and typical but he is just clumsy. He has lot of accidents and makes mistakes but they sure came in handy for Sam and for Alice to get back at the snooty woman.
The part where he shot an aspen in Mr. Wilson's mouth, he didn't do it to hurt him or upset him, he did it because he was afraid of his fake teeth biting off his fingers so he shot it in his mouth but didn't think he be upset until after he did it.
Oh yeah at the end where he presses the button, he didn't do it to get the snooty woman on the copier machine. He did it to show her he knows what button to push. Like a typical child, he runs when he sees he has caused trouble. No child likes being yelled at or punished and Dennis didn't want to get into trouble so he ran from it.
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