A slang term given to an MDMA (ecstasy) binge. Molly is a slang term for pure MDMA powder, but it has sometimes been adapted to include pills, especially in the plural form (example: We just scored a bunch of mollies). The term "Molly McBender" was derived as a play on "Molly McButter," the name of a butter substitute. These benders can last anywhere from half of a day to a week or more.
I somehow lost my shoes deep in a Molly McBender.