Andrade's Chin

How does he casually eat so many punches?

My theory is that he's not nervous about getting hit in the face so he keeps his body relaxed taking shots. That way his neck can work like a rubber band and help absorb the impact. His head will snap around a lot, but it's not nearly as bad as if he offered any resistance. His head rolls with the punches.

My other theory is that he's a caveman.

He's Mexican what do you expect

Teddy noticed that he seems to roll his head away from shots, maybe that helps.