A term for a girls ass. When a baby is born the baby is thrown at the mothers ass to make sure the infant does not have cancer. Men naturally like women with a fat ass so that the infant wouldn't be harmed in this act and so the infant would hit a fat squishy ass and not a bony dry ass.
A person who refuses to shout a round of beers. Guys named Benny or Rory are often referred to as tinass. There credit cards are covered in dust and often their wallets are brand new because no money has ever been inside.
A Tinass is the first person to yell “I’ll have one” then fades into the background come next round.