I guess what I'm trying to say is if you wear anything - robes, clothing, etc. - then I can see the AC 10 but to be in your cute bikini undies and still have about as much AC as you would have if you were wearing Light Armor seems weird.
In that case you are awarded an armor class of 10 due to either:
A) opponent laughing his ass off at you.
B) opponent distracted by your other "equipment" (either advantage or disadvantage)
C) you are all greased up, thereby making it touch for anyone to either hit or hold you
D0 you are a dwarf, and your opponent can't see beyond your beard to actually hit you
