1sleeveless garment (vest, waistcoat, singlet, tank top etc)
Examples
wǒ我zhǎo找bú dào不到wǒ我sān三jiàn件tào套de的bèi xīn背心。
我找不到我三件套的背心。
I can't find the waistcoat of my three piece suit.
背心反了，要翻一个面。
You need to reverse your vest, it's back to front.
你的背心前后反了，得翻过来。
You need to reverse your vest, it's back to front.