When I, an American, think of “knickers” I generally think of something like this (and I suspect I am not an outlier):
“Men’s Knickers – Khaki Twill,” via Historical Emporium, San Jose, California (“Authentic products and old-fashioned service” since 2003).
Across the pond, and Down Under, they think of something more like this:
“Know your knickers!” via Kayser Lingerie, Australia. Not for men.
But I’ve recently learned of two women’s-underwear brands doing business in the US that are trading on the British/Aussie sense of knickers. Which leads me to wonder whether we USians are about to adopt this sense of knickers into our retail vocabularies. (Or re-adopt, as I’ll explain in a bit.)