* As selfish as a hoarding squirrel. (This compares the person's selfishness to a squirrel's tendency to hoard food)
* As selfish as a black hole. (This compares the person's selfishness to a black hole's tendency to absorb everything around it)
* As selfish as a wilting flower. (This compares the person's selfishness to a wilting flower's focus on its own survival, even at the expense of others)
* As selfish as a single-minded predator. (This compares the person's selfishness to a predator's sole focus on its own hunt)
You can choose the simile that best suits the specific context and the level of intensity you want to convey.