To ask how your deal with know-it-alls??

[TrainsandDiggers]

You know the ones - the people who literally speak like an expert on every subject (even if the subject in question is your actual job/something you did a PhD in or something you have already done and they are about to, etc etc). The type the speak over you when you try to engage them in a conversation about the subject and/or just disregard your input even if you do get a word in?

I have someone like this in my extended family, so avoiding them is not an option. I find this behaviour absolutely infuriating though and find myself sat there seething.

Any proactive tips for managing this MN??

I avoid them like the plague.

My BIL is like that, especially annoying as we know half his facts are wrong - or made up. My secret weapon is my son, he can bullshit with the best of them, and likes nothing more than to wind his uncle up. You know my son has won when my BIL starts spluttering in annoyance. Now that I can laugh at him, it never gets old.

OP we may share the same family member, surely there cannot be two of them!!
I find drinking wine help or making something with my hands.

"Maybe we could hear from someone else for a change" works well for me!

I normally highlight my surprise in their knowledge sarcastically. Normally along the lines of "oh I didn't realise you were and expert in xx. When did you train in that?"

Normally shuts them up and sends them off.

We have a friend like this , I talk about a totally different subject when he starts his monologues, it used to really puzzle our daughter to hear it but he is totally oblivious.
He will also give you forensic details of everything, he won't say 'We went to France', he will describe every detail of the journey from the first lamp-post to the last, if one of them has a minor accident she'll say 'I tripped', he will turn it into CSI.

Tommy Two Shits is what I call it.....

If you’ve been for one, they’ve been for two.

Surely challenging them is more fun than ignoring them?

I like the idea of saying "ooh, I didn't know you had studied xxx, when did you do that?" or just "why do you think that?" and see what they say.

I suppose if it is just too boring then walking away must work!

Ah yes......the story topper. You'll never win I'm afraid.
I find pretending to nod off when they start quite effective

I have one if these in my extended family too. I use irony quite a lot when speaking to him after noticing that’s how his wife deals with him. I’ve also perfected looking at him like he is a strange looking snail whilst he’s talking and and saying ‘Errr no.’ just as he’s finished his spiel and turning to the next person immediately to start a conversation.

He’s too thick to notice.

Theres a woman like this at my work - we work in an open plan office and she butts in all the time even though she's in a different area.
Just today my colleague was asking me why she'd be getting double vision (I worked in optics for 7 years before this) and she butted in telling her what it would be and trying to decide her prescription just by looking at her eyes (hmm)

My ex husband is like this. It’s so unbelievably tedious.

It's even worse when the DO know something about the subject but are not socially aware enough (or love the sound of their own voice too much) to realise they are boring the rest of us to tears. Especially when someone keeps feeding them lines so they can expound further (narrows eyes at MIL). JUST SHUT UP!