Someone, female or male, who has a depression (aka sag) in either their breasts or hindquarters. It is usually used towards younger people, as old people tend to sag most of the time, and it is generally assumed that they sag anyway.

One who sags.
See that sagster over there? Man, her bra's really holding her up, if that wasn't there, she'd be dragging along the floor.
by Alfons Richter April 2, 2008
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Easily defined as a hollow cavity in the female breasticles, causing them to drape past the midsection. Additional tissue may be found to crinkle around the nipular region. Can be horrifically painful if not treated correctly. Treatment includes; lathering of Sudacrem to the affected area or (in extreme cases) taping the breasticle and removing tape in 3 hours harshly to smoothen the skin. An effective home remedy is available to create. It is a mix of vinegar, chili pepper, lemon juice and salt. Mix to form a paste which is applied excessively to the underboob.
In mama Jim's humble abode.

Jimmy: Mama, yo such a sagster!
Mama Jim: How dare you? Have you seen your moobs?! They be looking like prunes! Im'a rub that home remedy in yo eyes!
by Jimmy 4 life! December 31, 2019
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