A baby born under a bridge and lives there to this day.
Gerry is a bridge baby - he doesn't belong here. *Here being anywhere outside of under a bridge.
A person, young or old, with or with out addiction, that is homeless.
To describe something that is less than mediocre.
I saw a bridge baby swiping it's a ten off of the CVS shelves today, while I was going to get my prescription.
That bridge baby car got four spare tires.