Thorns or spiky armor should not reflect damage. They should cause damage when touched. Right? I guess the amount of damage could be contingent on the strength of hit. So in effect this would be reflection.
It seems logical, within fantasy tropes, that spikes/thorns and what not cause melee damage.
Reflective armor, especially shields, should bounce magic back at the attacker. This is a common trope. Mirror shield, shiny armor, etc...
I can't think of anything that might bounce back physical ranged damage. Like arrows and rocks. Nothing common among fantasy mainstays. Perhaps a kinetic absorption device? Vibration Armor? Vibranium (like capt. america's shield?). Amulet of shot/kinetic absorption? You'd have to get creative but you can make it work.
To stay thematic and not to get too wacky you'd have to get very creative in order to make an item/armor that reflects all damage. Note that Nethack is incredibly wacky thematically and it seems to work. For me anyway. I am thinking that this could be an emotional reflector. Amulet of Reflected Malice or Negative Reaction Armor. Ha! Maybe Newton's Armor (after Newton's 3rd law, every action has an equal and opposite reaction.) Or just go simple. Shield of Damage Reflection.
You can make your armors and what not do whatever you want mechanically as long as it works within your game universe thematically and you give the item a name that gives a bit of a hint about what it does.
Well man I hope that helps. I love design discussion.