Sagging

[Sarah]

A bending or sinking between the ends of a thing, inconsequence of its own, or an imposed, weight; an arching downward inthe middle, as of a ship after straining. Cf. Hogging.

[Sarah]

wearing ones pants around the hips so that they sag down and bunch up around the ankles. Originally, this was a prison thing that signified that you were another prisoners

[Sarah]

Hip-hop and gangster cultural fashion: Wearing one's pants below the level of the waist, sometimes below the level of the buttocks, with one's boxer shorts showing. The style may date back to around 1989.
The origin of this originally young, urban, black style is unknown. A commonly accepted origin theory was that is was an outgrowth of prisons, where inmates' clothing was often too large and sometimes no belts were allowed.
It may be related to skateboard/snowboard fashion.
At least one scholar thinks there is a tie-in with African culture.
There is also some evidence that a male showing his underwear-covered buttocks in prison was, at one point, linked to a desire for sex, or a mark that a prisoner was owned by another prisoner, sexually. Whether this kind of showing one's buttocks has any relation to sagging is unclear.
Some areas have begun to outlaw this style recently (2011). Apparently the objection is the amount of underwear shown.

[Sarah]

Too broke/too cheap to buy a belt.

[Sarah]

straiming of the ship which tends to make the middle portion lower than the bow and stern

[Sarah]

Sagging refers to the wearing of pants in a way that exposes the top portion of the underwear. Exposing more than the top portion of the underwear is considered a poor execution of the style. It is also inappropriate “to sag” when wearing briefs. Designer boxers are required. A belt is also required to prevent the pants from sagging beyond the upper portion of the back side. To sag with the entire back side exposed is considered poor form. The idea is to provide brief glimpses of the designer boxers as opposed to prolonged exposure.
Many myths and lies about sagging have been promoted to discourage the style. Sagging started around 1989 as a way for African American men to avoid what was perceived in the African American community as a homosexual look favored by white men in the mid to late 80s. The manufactures of the most popular brands such as Jordache and Levis did not manufacture jeans that were cut to fit the African American shape. In short, most if not all jeans would fit African Americans very, very tight and to the point that is was uncomfortable. White people tended to favor the tight fit while African Americans shunned it. To make the jeans fit in way that was more acceptable to African Americans, teen age kids and hip hop stars would buy there jeans two or three sizes too big. This started the trend of “baggy clothes.” Sagging became popular as well as a way to avoid the “homosexual look” of tight jeans. Also because the jeans were two or three sizes too big.

[Britney]

Kimaras [namie]

[PussyCat]

How niggys [in the hood] get caught after a murder [because they can] see the [glock] cause the jeans are to the thighs

[Sommer]

Sinking or bulging downwards under weight or pressure or through lack of strength.

[Tracie Lynn]

present participle of sag