There are many different ways to describe someone who is very thin or skinny. One commonly used phrase is "thin as a rail," but there are plenty of other synonyms that can be used as well. These might include "lean," "slender," "gaunt," "emaciated," "bony," or "scrawny." Other phrases that could be used to describe someone who is quite thin might include "skin and bones," "skeletal," or "cadaverous." While some people might be offended by these terms, it's important to remember that there's nothing inherently wrong with being thin - it's just a descriptor.