“Crazy Uncle Liberty” is a common phrase used on the Professional Left podcast, and in driftglass’ blog, and elsewhere (like Crooks and Liars, with h/t to driftglass).

Example:

https://crooksandliars.com/2016/03/brainwashing-crazy-uncle-liberty-and-how

or:

https://driftglass.blogspot.com/2012/09/three-cheers-for-crazy-uncle-liberty.html

Often a Crazy Uncle Liberty is some wingnut in your life. It can be a blood relative or an in-law, but doesn’t have to be. It may also be the character that people in your life like to pipeline email forwards from into your inbox (before social media), or now, often on Facebook or on Nextdoor or whatever.

I think a more recent-ish example of a public Crazy Uncle Liberty is that Pillow Guy…