The wording for activation is self-contradictory. You can activate this ability if you have the Angry condition… and when you do so, you can choose to gain the Angry condition if you don't already have it. Meaning that you don't actually have to have the Angry condition in order to activate the ability.
I'm unsure what the designers' intent is here.
Suggestion: change this text…
…to either this (if you need to be Angry to activate the ability)…If you have the Angry condition, you can activate this ability (no action) when making a dice roll and get a boon to the roll. You can also choose to become Angry when you activate the ability, if you’re not already.
…or this (if you don't):If you have the Angry condition, you can activate this ability (no action) when making a dice roll and get a boon to the roll.
You can activate this ability (no action) when making a dice roll and get a boon to the roll. You can also choose to become Angry when you activate the ability, if you’re not already.