Comeback Kicks

Whenever the crowd cheers you, if you have less

than each other hero, you may destroy this. If you do, gain 1 action point.

Battleworn

Rulings

From the Compendium of Rathe release notes

Comeback Kicks’ first ability triggers whenever the crowd cheers you, regardless of whose turn it is. This is an optional effect: when the triggered effect resolves, you choose if you want to destroy Comeback Kicks provided you have less life than each other hero. If you destroy it this way, you will gain 1 action point.
When resolving Comeback Kicks’ triggered effect, there is no priority between any of the effects generated (e.g. destroying it, gaining an action point).

Keyword notes

Battleworn - Equipment that wear down after each time they are used to defend. If you defend with a card with Battleworn, put a -1{d} counter on it when the combat chain closes.

When you defend with a card it remains on the combat chain until the chain closes, therefore you cannot defend with an equipment multiple times on the same combat chain.
A -1 counter stays on the card until the card is destroyed or the game ends.
If the defense of a card that is defending is below zero, its defense value is considered to be zero.
When this card is destroyed, it is sent to your graveyard. (Not when it has 0)
When this card is destroyed, it is sent to your graveyard.
If the defense of a card that is defending is below zero, calculate as if its defense is zero.