I've always been interested in the AC/DC contradiction, known for being a no nonsense just about the music band, but Angus in the schoolboy outfit may be the most recognisable in rock, definitely outside of KISS, and a big stage show full of props and theatrics. It's not something they've ever been called on I don't think.
Yes, it did/does defy a 'jeans and t-shirt' no-nonsense band having a 'gimmick' - but as I understand it, initially suggested by his sister Margret as a joke, Angus saw the defiant cheeky angle in the costume as he hated school...
Moreover, while most Aussies just laughed along with it, the US audiences went nuts over his costume as, unknowingly to AC/DC, it represented something different to them as only elite wealthy Americans could afford to send their kids to schools that had uniforms...