seamy side

The sordid, unattractive aspect of something: “Lying and stealing are part of the seamy side of life.”

The sordid or base aspect of something, as in This nightclub certainly shows you the seamy side of the community. This term refers to the wrong side of a garment, revealing the stitched seams. Shakespeare used it figuratively in Othello (4:2): “That turn'd your wit the seamy side without.”