STS Share definition Flag (N.) An acronym that stands for "Saggy Titty Syndrome". This usually occurs with age. However, men with klinefelters syndrome have been known to develop this disease. "Dude, look at Mrs. Wolfe. She is infected with STS" STS by Mr. Jab May 25, 2006 0 0 Get merch Get the STS mug. Buy Now — $32.95 See more merch