Don't Laugh

If you substitute the word "brain" for pain the result often makes sense, but not as much the other way around. Some examples...

No brain, no gain... (a little obvious)
He's such a brain (low hanging fruit, yes)
I met a real brain in the ass today (all kinds of possibilities here)
My chiropractor is helping with my chronic brain (could be true)
Welcome to the house of brain (marketing potential)
He had a brainful expression on his face (I've seen that before)
Foot brain, leg brain, tooth brain, back brain, the list goes on (you know it when you have it)
Lose the brained look, whiner (perhaps after a fight)

Now for the other side, I don't know....

I'd like some pain and eggs (belly pain?)
Don't be such a bird pain (huh?)
The country now suffered from a pain drain (who doesn't want that?)
Painiac (sounds strange)
I've got this incredible pain right behind my eyes (might work)