Ummm…to all my Spanish-speaking wooters, is there a slang term for “underpants” in Spanish? I know the official translation for “underwear” is <>, but I’m sure there’s another (non-R-rated) term for it?
calzoncillos?
You don’t sound very certain. 
I’ve just been calling them pantalones de baja. heh
Chonies… (Cho - knees)
not sure if that’s spelled properly, but it’s what my (m)ex-girlfriend used to call 'em.
Merriam-Webster agrees with no1.
The Wikitionary says it may vary depending on region:
calzoncillos m. pl., anatómicos m. pl. (Paraguay)
fundillos m. pl. (Chile, dated - current usage : calzoncillos),
gayumbos m. pl. (Spain, colloquial)
interiores m. pl. (Venezuela)
pantaloncillos m. pl. (Colombia)
May be interesting however to consult the Doubletongued Dictionary …
Growin’ up in AZ; I heard this used a lot to refer to 'em - usually in reference to boxer shorts . . .
Urban dictionary syas “Chonies” as well. Thax, all.