It’s called a red bomb, 紅色炸彈 (hóng sè zhà dàn).
Red bomb, 紅色炸彈 (hóng sè zhà dàn), is the Chinese nickname for 喜帖 (xǐ tiě), meaning wedding invitation.
Chinese wedding invitations are red. If you receive a wedding invitation, you’re supposed to send money whether you will attend or not. Therefore a red invitation is a thing that costs money, like a bomb that cause damages.
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