on the back of a postcard—(in the phrase “fit on the back of a postcard”) said of the insignificant amount of one’s knowledge, information, etc.:
- The phrase “fit on the back of a postcard” comes to mind but a postcard would probably be too large to list out all that I know about art.
Cf.: on the back of a postage stamp—used as a more emphatic variant of the former:
- Alas, my list of strengths will fit on the back of a postage stamp.
on the back of an envelope—(of plans, calculations, etc.) executed in a simplistic and speedy way and usually in need of more work (also: on the back of a fag packet):
- He has made decisions sketched out on the back of an envelope without proper consultation again.