My sister's husband really ticked off this mamma bear, on Mother's Day no less. BIL and sis have no children and that's a good thing. She is a great aunt. BIL has moments of being a good uncle but they are totally undone by his lack of ability to see the world with shades of gray- everything is clearly right or wrong and you stand no chance of changing his mind.
So, today we were at brunch with them and ds1 made a bad choice. A catastrophic, sociopathic choice? No. Did BIL act like ds1 did? Yes.
Brunch was over, check was paid, we were just about done talking. Ds1 had been sucking up ice cubes with his straw, like using the straw as a suction cup by sucking in his air. He got an ice cube picked up and released it into BIL's empty cup. Not a good, mannerly thing to do- that's a given. But BIL went off on ds1. "what the he$$?! Why would you do that???" then more lecturing. A WTF and move on would have been understandable but ds1 wasn't doing it to be a jerk and he got it. The irrate lecture was over the top. Ds1 loves this uncle and was really upset.
Know what I did? Kissed my mom goodbye, thanked my sis and scooped up the kids and left. If I stayed, I wouldn't have said anything good. Really, I get it, ds1 made a dumb choice. But, dude, your cup was empty and we were leaving! He didn't spit into your drink, like you said he did. Have some perspective - and tone down the dramatics. You made my kid cry and made my day far less good.
Eta- he's 43 so not some kid that might have a slightly more valid lack of kid skill set.