The phrase "thankless wretch" is often used to describe someone who is ungrateful and undeserving of appreciation. However, there are several synonyms that can be used in place of this phrase. Some alternatives include ungrateful ingrate, unappreciative brat, self-centered egoist, or thoughtless miser. These terms convey the same idea of a person who takes others for granted and does not show gratitude for their efforts. While the phrase "thankless wretch" may be common, using alternative terms can add variety to your writing and communication and help convey your message more effectively.