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!