The Alpha effect?

[HuhWhatNow]

I'll just start by saying my DH is a top guy. Perfect. He's loving, loyal, does more than his fair share of housework, parents just as much as I do, we never argue, spend every spare moment together and he even buys his own family's Birthday and Christmas presents!

However, for one night every couple of months BIL stays over. He's a great bloke and we're a close family so he's very much welcome. They go do DH's hobby all day Friday and Saturday (I'm breaking all the MN rules here naming the hobby but it's Gold Panning!). Here's the thing. BIL is under the impression that DH and I don't get along. That we fight and argue all the time when it's simply only when BIL is here, DH somehow decides to act like Billy big bollocks and gets nippy with me. Something which I do not accept. Ever.

Tonight's was a silly little thing. I told DH he'd need to move something he'd plugged in down my side of the bed or I'd stand on it (during one of my many trips to the loo in the night). He was rude back and said it wasn't an issue it being there and it didn't bother him. Well it fucking bothered me, being that I would be the one affected, not him! He's also been fine with taking my car (he wrote the family one off in a his fault accident) for his hobbies and saying, "It's okay, it's not a bother. You can walk to work" without even thinking and when told, caring that it would bother ME.

He is never like this except when BIL is around. I don't get it. Is it and Alpha/Beta male type thing? He's not mean, cruel or abusive, just... different. A bit of a dick at times.

Do this happen with other men? I'm ashamed to say that I blew up on him tonight and told him straight, right in front of BIL that he'd "better stop being a dick like this or he'll not be having his pals round again like the fucking teenager he's acting like!"

That's pretty weird. Is he little bro or big bro?

Neither. It's his sister's DH.

Oh and to clarify, it's not DH picking fights, it's just him being a bit rude or insensitive maybe? Saying something that makes me stop and give him a WTF did you say? face.

Sounds like he feels a bit insecure round your bil and it makes him have to act like the big dick in the house. I wonder if your bil has got views about men who are under the thumb which come out when they spend time together and your dh is over compensating making sure he doesn't seem under the thumb.
Have you just asked him about it when bil isn't there. Seems like a clear difference and a regular pattern, if you normally communicate really well can't you just ask, then he can't pretend you don't both know what he's doing next time

I've spoken about it before and because it's nothing particularly obvious, he claims he's not doing anything and I actually believe he is completely unaware. It's the weirdest thing. He acts like I'm the one with an attitude for being mad about whatever he said.

BIL is a nice fella. A blokey bloke for sure but not a mysoginistic prick or anything. Just a beer, football and power tools type.
DH is tea, hobby and hire a tradesperson type.

I think insecurity could be it. Whether DH is aware at all is another matter.

He is totally trying to show off in some immature way to BIL. That he is his own person, doesn’t need to listen to you. I do notice men can act like that when they meet up sometimes. My DH does it on occasion. I usually try tell him to knock it on the head privately first. That doesn’t work, then he does get a dressing down regardless who is there.

Hmmmm, sounds like you need to hold a mirror up for him so the penny can drop and his self awareness can kick in.
Can you pocket a comparable example of him being considerate/inconsiderate in the two different situations and then when all is calm and bil isn't there you can say 'here is what I mean, this is a classic example' then you can kindly point out that the effect of his unconscious change is to make it look like he has a shit argumentative relationship with his wife and he needs to catch himself doing it so he can be more his true self around bil.
My dh has this effect a bit on our neighbour, we are building our own house (both of us, with our own hands, but I don't have this effect), our neighbour is not remotely practical but is well off so will hit tradesman at the drop of a hat. But when talking to my dh he gets all blokey about diy skills etc. Dh isn't actually interested in diy is only doing lots of it out of necessity and would rather talk about aeroplanes so this decibel comes from the perceptions of the neighbour. I guess it's an internalised view of what men should be like leaking out.

Hire not hit! He isn't violent to his hired help! 😆