Definition
An indirect way of expressing that the addressee is gullible.
Origins
In reference to George C. Parker, an infamous conman who successfully duped his victims into “buying” the Brooklyn Bridge.
How People Actually Use It
This phrase came about after a Con-man by the man of George C. Parker sold the Brooklyn Bridge twice a week for 30 years. LINK: https: // en.wikipedia.org/wiki/George_C._Parker
"Person 1: Hey I hear the Earth is a Globe. Person 2: OH Yeah? I have a bridge to sell you /I have a bridge, do you want to buy it?"
Source: Urban Dictionary