All uncles are weird. But being an uncle is an exogenous event independent of any quality you have, weirdness or otherwise. So statistically it looks like a monumental fluke that all the weird people turn out to be uncles.
In reality it’s the uncleness that causes the weirdness. And more than that: even totally normal people who happen also to be uncles turn onto weirdos precisely when they are around their nieces and nephews and here’s why.
An uncle is basically an anti-parent. Not anti- in the sense of anti-aircraft or anti-American. More like antimatter. Because an uncle looks at his brother or sister’s family and basically sees everything that his own family is not. Good or bad. Especially in terms of the children.
And just like boys socialize by playing up and exaggerating differences as a mechanism for toughening up each others’ weak spots, the uncle can’t help but play that same role with the nieces and their parents. Niece is too sensitive because she is too sheltered, uncle brings the missing risk to the party. Nephew thinks he’s tough because he can push around his younger sisters, uncle gives him a taste of his own medicine.
Then there’s spy mode. Uncle wants the inside scoop on his brother/sister and spouse so he asks neice/nephew strange leading questions. Your uncle is an outsider who has just enough of an inside track to feel comfortable poking around where he doesn’t belong.
But whatever mischief the uncle is up to, the actual effect is that he comes across as a weirdo to his neices and nephews.