(jocular) wedding invitation (lit. "red bomb", because wedding invitations use red paper, and invitees are expected to give a substantial sum of money as a wedding gift)
Definitions (CC-CANTO)
wedding invitation (slang)
Definitions (粵典–words.hk)
名詞
婚禮請柬，通常用象徵喜慶嘅紅色信封裝住，邀請收信人出席之外仲要畀人情 wedding invitation (a reference to the red envelope containing the wedding invitation and to the donation that must be made to the couple at the wedding banquet)
noun, figuratively, humorous, informal
red-coloured wedding invitation card (which implies a loss of money for the receiver in the near future, from having to give a red packet upon attendance) (syn.) 喜帖