Next time you are disappointed about the way you have been treated by someone, instead of flying off the wall, sleep on it and see how you feel the next day.
Living in the present can apply to this sort of thing. Actually, try just totally forgetting an issue or conflict instead of rationalising it. Of course there is a place for thinking it through, but just for once, try your hardest to (a) totally accept the blip as just that – nothing worth worrying about – then (b) try to just let it go out of your mind, willingly, lovingly. As you do this, and it will be a repeated thing, because the thought will keep coming into awareness again and again, as you do this, use breath awareness (for example) to help you be in the present rather than the ‘past’ of the thought that is presently bugging you.
In this way, being forgetful is quite liberating and useful.