Pretty much everything you need to know about taking criticism can be summed up in this article:

• Relax (You’ll be surprised how fast you will recover.)
• Strengthen your neck.
• Practice (Get hit a lot.)
• Breathe.
• Try to absorb the blow, roll with the punch
• Remember to keep your mouth shut
• Protect your vulnerable areas
• Keep your balance

(Thx to Mike Monteiro for the idea: “the skill I picked up in [art] school that turned out to be the most valuable was learning how to take a punch.”)