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1.
Underutilized acronym providing an implied warning, and therefore appropriately stigmatizing, basement apartments aka man/rape caves, leper lairs, basement brothels, dick dens, bottom dwellers, whore holes, bang burrows, pig pens, sadist sanctums, titty tunnels, horny haunts, comic geek coves (aka CGC), hairy hubris hovels, vagina vaults, cunt cellars, cryogenic creamer crypts, insane arcane no refrain henbane subterranes (and nearly any combination thereof), nookie nests, ho hovels, and ateliers among other names.

In the city of Chicago, BSMTs are sometimes simply referred to as a cubbyhole when said BSMT is occupied by a Chicago Cubs fan, though even more so when said occupant is NOT a Chicago Cubs or even a general sports fan.
Example 1

GIRL: Girl, what were you thinkin' goin' back to that BSMT with Little Stevie Wonder?
TRANNIE: Uhhhh huhhhh, 'cause I heard he gave as good as he got!
GIRL: Sheeeeeet, you must be meanin' some low down bi-oral, 'cause they ain't call him Little from being Omar's cousin.
TRANNIE: I'm tellin' you right here, it was insane no refrain subterrane from midnight 'til more-nin!

Example 2

SHE-RA: Hello? Is this emergency services? You've gotta help me! I was with some guy, and he just attacked me!
DISPATCH: Where are you? Are you in danger? Do you need assistance?
SHE-RA: Don't know where I am, creep took me to some BSMT and went all Hordak on me! Had no idea He-Man could fit that far, and I can't get him out!
DISPATCH: OK, let me know the cross street and stay there. And whatever you do, don't turn back into Princess Adora, that will only exacerbate the pain!

Example 3

OLD CO-WORKER TEXT: that davich guy knows his music but must have grown up on a short bus. the dude is creepy.
YOUNG CO-WORKER TEXT: AFAIK IRL he rolls out ADA back to his BSMT CGC 4 DD SHIELD MODOK BMB JMS OMAC CBPG then ABBA JLO UB40 ACDC KISS B52 REM back to ADA. GGP NRN
OLD CO-WORKER TEXT: BSMT LMAO TTYL ;)
by modoklover June 15, 2010