Acronym for tits by fat. Used when a fat girl (or her almost always equally fat boyfriend) attempts to brag about their large breasts. In reality they are extremely saggy and often accompanied by a disgusting set of stretched and contorted nipples.
Tom: Dude, Cynthia is the best girlfriend ever. Her tits are massive!
James: For Christ sake Tom, she weighs 350 pounds. That damn pig has a severe case of TBF.