on him like ugly on an ape

On him like ugly on an ape is an idiom which is referring to describing a widespread and thoroughly prevailing situation or state of affairs. When someone says someone or something (usually a person) is on him like ugly on an ape it means to exist in this common manner because most apes are considered to be ugly in the sense of their appearance. On him is in reference to being interested in this person or pushy in regards to everything they do or say.