Now that I have your attention, I need a clarification on the term from those who speak Brit instead of Mercan.
Does knickers mean strictly women’s underclothing or is it used for men’s as well?
Does knickers mean strictly women’s pants or is it used for what’s up top as well?
Would someone speaking Strine or Kiwi have a different opinion?
Ozstrine here.
Knickers always means women’s pants and does not refer to bras (or what’s up top)
Men’s pants are colloquially called ‘jocks’, never knickers.
Undies can be gender-neutral. 
Wot she said.
Yeah, basically knickers closer in meaning to panties than to underpants.
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.
Brit here. What the Aussies said. Knickers clothe the lower pantal area on a lady.
Me too and I don’t know why. ‘Pantyhose’ doubly so. Wonder what that’s all about?
Oh dear - let’s not get started on “fanny packs”.
Yeah - in England we men wear pants under our trousers and the ladies wear knickers. At what point a pair of knickers (always a pair) becomes a thong, I am not sure, but many females wear those instead of knickers. Of course some women don’t wear anything at all.
<anecdote> When my wife worked in a Special Care Baby Unit, I was a regular visitor, picking her up after her shift. Several of her colleagues were young and attractive and it was a bit tricky there for me, because I knew that, with the high temperature in the nursery, all of them wore stockings rather than tights (too sweaty) and many wore no knickers either.<anecdote>
“Knickers” in the UK is generally used more for comic effect (e.g., it’s used as a mild replacement for swearwords, as in “Knickers to that”, or jokey references to those strange people who steal underwear, known as knicker-nickers). It implies something rather less compendious than bloomers, but still more sensible than racy flimsies.
Predominantly applied to women’s underpants, it might occasionally be used of men’s, again more comically. Generally, they would normally be “pants” or underpants.
In Northern Michigan, “knickers” refers to pants that buckle below the knee, worn by girls & women at the National Music Camp, as depicted he–whoops, let’s not do a google search on that while at work, now…
Southeast Missouri here:
Nobody uses the word “knickers” for any reason, unless they’re talking about the men’s garment popular c. 1900.
The garment that covers your legs is a pair of pants, or a pair of jeans if they’re denim. No one says “trousers.” From time to time someone may jokingly say “britches,” especially when their child is acting too big for hers.
The garment you wear under your pants depends (heh) on the context. My wife and I are both wearing underwear. The garment under my pants is boxer/briefs. The garment under my wife’s pants is a pair of panties.
In Indian English, the word ‘knickers’ is used to mean some manner of shorts, typically for boys. This is just in my experience (and the word is falling out of favour), but some casual Googling shows that I’m not alone in this.
Oi. Serves my right for not doing a search first.
That was one of the reasons for the questions. Those who care about such things have decreed that “panties” sexualizes women’s underwear (Well, duh!) and we should not use the term. Dictionary.com cites the first use was 1845, so I’m thinking they’re a little slow off the mark. Unfortunately, where I read this had no recommendation for the substitute.