by far the funniest scene: in the beginning when they are trying to find the friend's house and the dad goes "fricken sacagawea back there is givin me sh** directions" (or something along those lines)
my other favs were: "like father like son" "BRING 'EM" and "welcome to my world" oh God i snorted on that one
Best part is definitely the last scene when the RV topples over and completely crushes, and I mean pancake flattens, the police car. The complete destruction of the car was just too ridiculous. Also the scene where Robin Williams strangley walks into the lake and emerges psycotically riding his bike---the sheer craze that had overcome him to give him the powers to do this was too much as well.
i always crack up when the gorneckys throw the guy off the bus for stealing the laptop and he says "I found it" and then mary jo just sticks her head out and says "well know you lost it" the delivery is priceless