Acronym, standing for Titties by Default. Refers to the massive protrusions of fatty tissue present in the chest area of overweight women, and occasionaly men. Not to be confused with BAT's (bomb-ass titties
), Titties by Default are not composed of breast tissue, but rather an inevitable dispersion of fat cells throughout the bodies of those afflicted. While TBD's are responsible for giving fat women a false sense of confidence and self worth, they are equally capable of deceiving unsuspecting onlookers, and masquerading as BAT's.
Stel: "Holy shit, that girl eating the nacho plate to herself has PHENOMENAL breasts. I can't stop staring"
Me "No dude, they're TBD's. If I was 3 bills I would have phenomenal breasts too."