During the winters in China, it is very common (almost necessary) to wear long johns or long underwear. Being a foreigner, I’m not used to wearing long johns, but there was one day when the weather was as cold as -20 C. It would have been crazy not to have been wearing long underwear that day, and indeed I was crazy enough not to. I was even keen enough to tell my Chinese friends this. Funny enough, instead of telling them that I wasn’t wearing long johns, I had informed them that I wasn’t wearing any underwear.
A common mistake by foreigners is to call long underwear “nèikù” (内裤), which in Chinese actually means “underwear”. The right term to use is “qiūkù” （秋裤）。As a foreigner speaking to a local the Chinese, it is quite embarrassing but common to tell him/her that you’re not wearing any underwear. Even more embarrassing is to ask your Chinese friends whether or not they’re wearing underwear!! Don’t make this same embarrassing mistake!