... as in wearing no pants. Where does this expression come from?
From Wikpedia. Going commando (or to go commando) is the phenomenon of not wearing underwear under one's outergarments in public. In American slang, this phenomenon is also referred to as Freeballing (in the case of males not wearing underwear) and Freebuffing (in the case of females). A 2004 study of 7,000 people by the New York-based clothier Freshpair revealed that 9 percent of men and 7 percent of women go commando on a day-to-day basis, with an even higher percentage doing so on a semi-regular basis. In British English, the use of commando as a verb is a relatively recent phenomenon but increasingly common. The phrase and phenomenon is often used in a declaratory way (particularly by young women) to covertly create a frisson of sexual excitement or amusement amongst friends, sexual partners, etc. Modern British social mores generally recognise "going commando" as a "playful" behaviour (akin to a mild form of exhibitionism), and one that does not necessarily demonstrate an overtly sexual intent. However, it has to be recognised that in many cases there is a recognisable sexual element to the behaviour.
"The origins of the phrase are uncertain, with some speculating that it may refer to being "out in the open" or "ready for action." According to Engber many soldiers do go without underwear to "increase ventilation and reduce moisture."" Sounds plauseable but I was hoping for something weirder.
Indeedy. The Vietnam Conflict was an attempt to keep those murdering Commie Bastards from corrupting our youngsters. And ensuring large profits for the MI Complex, of course; its the American Way. Mention Domino Theory today and what do you get - asked if it's about pizza.