A term to describe the passing around of a drink (usually
alcohol) in which everyone's mouth drinks from the same opening. This is very common in situations where people are looking to drink fast and
don't have the luxury of cups.
The term is derived from the disease Mononucleosis (mono), otherwise known as "the kissing disease." Which is transferred by saliva from an infected
person to the lucky recipient.
Monorail is also taken from other phrases such as "jump on the band wagon." However, this mode of transportation is a one railed
train first invented in the early 1900s.
The phrase then is said to cue someone to take a drink, while joking that they going to get mono because another
person, or many, have already drank from it.