You cannot do the following when looking at an armorstand:

• Throw throwable items (snowball, enderpearl, etc.)
• Throw an ender eye
• Charge a weapon (bow, trident, crossbow, etc.)
• Equip gear onto player if that gear is on the armorstand
  • EX: If you equipped an armorstand with a helmet and then rightclicked it with a second helmet, the second helmet won't equip to the player, but will make the equipping sound.