I don't have any that I use all the time, but on occasion, I have a few "go-to" ones:

Were you born stupid or is this a recent development?

You don't have to be scared to get whooped!

I'd like to buy him for what he's worth and sell him for what he thinks he's worth

Wish in one hand and spit in the other and see which one gets full quickest

Even a blind squirrel is right twice a day

You're a liar and your feet don't match

The nut didn't fall too far from the tree

Happiness is a choice, not a consequence

There are no stupid questions, just stupid people that ask questions

He's so crooked that when he dies, they'll have to screw him into the ground

I'm not conceited, just convinced

I think extremist should be shot

Never take dieting advice from someone fatter than yourself (lots of applications on this one, like advice about raising kids from someone that doesn't have kids, etc)