Quote Originally Posted by Misterwhisper View Post
Q86

Can you choose not not use certain defenses at the time of an attack.

Ex.

I want to use hellish rebuke or armor of agathys or whatever and I am holding a shield. Can I choose to not add the bonus from the shield to my ac?

Or

If I have THP do I have to use them or can I choose to take the damage myself?

Or

Can I choose not to use arcane ward’s HP and instead take it myself to save the ho of the ward?

R86: To add to the reply from Chronos: The text of shield states, "Wielding a shield increases your Armor Class by 2," so a character could simply choose to not wield the shield and thereby lower their AC by 2.

The RAW state that an attack is made against a creatures AC, and as far as I could tell there's no allowance for a creature simply allowing themselves to be hit. So "check with your DM" is going to be the answer to that part of your question.