damp squib

/D AE1 M P S K W IH0 B/
noun
  1. 1

    A firework that fails to go off, due to wetting.

  2. 2

    (by extension) Anything that doesnโ€™t work properly, or fails to come up to expectations.

Source: https://en.wiktionary.org/wiki/damp%20squib