The bug

Certain projectiles, when thrown or launched at an Enderman, will not cause it to teleport away, or will hit/interact with the Enderman even though it teleported.

The following projectiles hit the Enderman, and the Enderman will not attempt to teleport:

• Splash Potions that do not deal damage
• Splash Potion of Poison
• Any Lingering Potion
• Any type of Firework Rocket, from a Crossbow or Dispenser, direct hits or splash damage
• Falling blocks or anvils
• Dragon fireball
• Bottle o’ Enchanting

The following will hit, damage, or be destroyed upon contact, and the Enderman will teleport:

• Fire Charge fired from a dispenser and Blaze fireballs
  • Projectile is destroyed
  • Enderman will be set aflame
• Ghast fireball
  • Fireball explodes
  • Enderman only takes damage if it hits something nearby instead of a direct hit
• Splash Potion of Harming
  • Potion is destroyed
  • Enderman dodges and is unharmed from both direct and indirect hits
• Eggs and Snowballs
• Splash Water Bottle and Lingering Water Bottle
  • Enderman takes damage from direct and indirect hits, but still teleports
  • The knockback they receive is not removed, causing the Enderman to appear to jump when it teleports and causing it to land around a block away from its teleport location
• Shulker Bullet
  • The projectile is destroyed
  • The Enderman does not take damage, but still receives the Levitation effect.
• Wither Skull projectile
  • Projectile successfully hits Enderman and deals damage
• Ender Pearl
• Wind Charge
  • Wind Charge explodes, and the Enderman teleports and is unaffected
  • Enderman does not teleport and is knocked back from the blast if it hits nearby

The following will be successfully avoided by the Enderman, and the projectile will continue in its trajectory:

• Any arrow type fired from a Bow, Crossbow, or Dispenser
• Trident
  • Arrows and Tridents may appear to wobble or shake when coming in contact with an Enderman. This doesn't seem to change their location or momentum, but will change the direction they're facing temporarily before reverting.
  • If a group of Endermen are too close together, shooting an Arrow will only make one of two of them teleport, and the arrow will pass through the rest harmlessly.
  • Tridents will only cause one Enderman to teleport, no matter how many it hits or how far apart they are.
• Llama spit

Other notes:

• If an Enderman fails to pick a new place to teleport to, the projectile may just bounce off.