Pathfinder doesn't allow you to do unarmed strikes with any body part the way 3.5 interpretations usually do.
The monk unarmed strike section says that you can attack with fists, elbows, knees, and feet.
Even with the most liberal interpretation of a quenching amulet of mighty fists only those body parts would be immune to fire damage. I'm also pretty sure that non-monks have a more restricted unarmed attack list that's defined in the core rules.
But unarmed strikes have always included more than just punching things snarky ketaro.