anticlimax

2. A sudden change from a serious or exciting moment to something silly or ordinary.

The play built up to a dramatic speech, then ended in an anticlimax with a sneeze.

3. A weak or disappointing finish to a story or event.

After weeks of practice, the final game was an anticlimax because the other team did not show up.

4. The use of a dull or ordinary idea right after a grand one, often for a funny effect.

The poem praised the hero's courage, then mentioned his smelly socks—a funny anticlimax.