My MIL has this thing she'll say when my son is acting crazy, limbs flailing out with energy like one of those wavy arm, air filled tube guys they have outside of tire places except his flailing is accompanied by loud noise. She'll say, "You're acting just like an almost four year old!"
And it really is a wise thing to say.
My kid is a really good kid. He doesn't have tantrums (much) and generally isn't a little rude demanding whiner (much). So when he does those things it is all too easy for me to have a reaction of, "What the hell is wrong with you?!" I expect more from him because he usually acts much more mature than his age. And that really isn't fair to him, especially in those moments he is frustrated and freaking out about something that only an almost four year old would freak out about. So it helps to remind myself of his age.
When you are at the end of your patience reserves, saying, "You're acting just like a (insert child's current age here) year old!" in an exasperated tone immediately diffuses the situation. It is funny because they are that age. And it reminds you to cool down too. To let them be that age. And (perhaps most importantly) that they won't always be that age.
What do you do when you are out of patience?