I actually might be able to provide some insight to this. My wife is Balkan and the first time I called her a "Silly Goose" she became madly upset. It turns out in her language the phrase "Glupova Gusko" (Stupid Goose) is a common insult. It is considered incredibly harsh in her culture. My guess is that the phrase "Silly Goose" is borrowed from a Slavic Language and lost its harshness when it moved into English.

The silliest person I know was deadly serious and no-nonsense at work. Their silly side only came out among friends. Maybe you just need to befriend a goose?

Because Honk?

They sound almost as silly as a donkey, which shares the moniker.

This is why you have to run when you find a goose among your ducks.

I thought up Goose as a superhero for a street level setting, essentially she's a tough scrapper, easy to underestimate, and is really good at blending into crowds or workstaff. Mistique without the mutant shapechangey stuff.

I got bitten by a goose once as a kid. I fear them since then, so they really are a force to be reconned with.

I am damned well sure I could take one (would get battered, but I'd come out on top, just need to get it by the neck once)

The problem is those fuckers live in flocks

Well, they look kinda silly when they aren't trying fight something

i think this would probably explain the phrase "silly goose"

I imagine the whole point is to say that someone is "sillier than a goose" famously known for, not being silly at all. Arguing that you are so silly, that you look like a goose being silly.

If you got a problem with gooses then you got a problem with me, and I suggest you let that one marinate!

Here's your silly goose right here

https://youtu.be/u08E7c-FRbU?si=c65hmJSQNHRCPlpI