I’m Australian and male and I might refer to my underwear as knickers, in a jocular way. Probably have done so at some point.
I don’t wear jocks - I wear trunks, and have do so exclusively for at least a decade - so I would not call my underwear jocks. I’d generally just say undies or underwear, trunks if I needed to be specific.
I know that if a Brit says pants they mean underwear, and I know if an American says pants they mean trousers. Me, I would just say underwear to avoid confusion.
I do call female underwear knickers, and the Americanism panties gives me the creeps. Also, shorts are outerwear, the underwear is called boxer shorts. And while we’re at it, pissed means drunk, pissed off means angry.