The phrase "sad gecko" can be replaced with a number of synonyms to give it a slightly different connotation. For instance, you could use "melancholy lizard" or "downhearted reptile" to describe the same emotion in a different way. Other alternatives might include "mournful skink," "blue iguana," or "glum chameleon." Each of these options offers a slightly different take on the idea of a sad gecko, perhaps emphasizing different elements like the creature's color, movements, or habitat. Ultimately, the choice of synonym will depend on the context in which it is used and the specific mood or impression that you want to convey.