An adult who still gets money from their parents. Being under your parents car insurance or cell phone plan when you're over the age of 22. A person who continues to get rent money, grocery money, etc from their parents even after they've graduated college. This person makes poor decisions with money because they know they have their parents to bail them out. This person will continually deny sucking their parents tit because it is embarrassing to admit they can't lead an adult life. Parents who have a titty baby will likely never be able to retire as they will continue to support said titty baby well into their retirement years. By the time the parents die, there is no milk left and therefore no inheritance for the other children.
Billy: How does Brent afford to drive that Benz on his 15 hour/week job?
Marty: His parent's bought that for him when he turned 24 and they pay his rent and cell phone bill.
Todd: That titty baby is still breast feeding at 27.
Marty: His parent's had to sell their retirement house because of that lazy son-of-a-bitch.