If the angry thought has gone, but you still have it in mind, you could always note "remembering, remembering" until it is gone. Often I find an unwholesome thought comes back in a sense as I remember it involuntarily. Or if you have a chain of thought leading on from it, e.g why did I think that?, I wasn't being mindful!, I should be more careful next time ect. you could establish mindfulness on that.
Commentary states that mindfulness can never be 100% in the present moment due to momentariness (not to say it isn't practically in the present moment), so if you are so inclined bear that in mind.
"If beings knew, as I know, the results of giving & sharing, they would not eat without having given, nor would the stain of miserliness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared."