Some Phrases I Don't Understand

The proof is in the pudding.
Huh??

...beat you like a red-headed stepchild.
What does everyone have against red-heads and stepchildren?

I don't give a rat's ass.
I guess a rat's ass is not that important. But to the rat it is!

Those are selling like hotcakes!
Do hotcakes really sell that fast? Or is it only at IHOP?

He's as white as a sheet!
Well, nowadays sheets come in all sorts of colors. Just go to Wal Mart and see for yourself.

Looks like your goose has been cooked.
I don't even have any geese.

Love thy neighbor as you love yourself.
That's some good advice...unless you are suicidal or clinically depressed.

That which doesn't kill you makes you stronger.
More like, that which doesn't kill you, will put you in the hospital.

Knock on wood.
Does knocking on wood have some sort of special power that I am unaware of?

...by the skin of my teeth.
Do teeth even have skin??? Yuck!

Keeping up with the Joneses.
Who are these Jones people and why do we need to keep up with them?