ne pas casser trois pattes à un canard

Etymology
lit. 'to not break three feet of a duck'; because ducks are bipeds, it would be quite out of the ordinary to break a third foot. Another explanation is that it derives from the similar-sounding, in allusion to a horse rider: only a daring rider would risk pushing his horse to the point where it breaks one or more legs.

Verb

 * 1) to be nothing to write home about to be mediocre; to be nothing out of the ordinary; to be nothing special