Originating in South Australia, this term refers to Minda Incorporated, an organisation established in Adelaide in 1898, to support individuals (particularly children) with intellectual disabilities. It became popularised in primary school playgrounds, employed as an insult.
The term is often directed at the intellectually disabled, but can also be used to belittle family, friends, or complete strangers (though the latter depends on one's fluency in bogan
Person A: oh, shit, I just spilt tomato sauce all over my extremely tight, acid wash jeans!
Person B: ah, ya fuckin' minda!