It is or was common for a crowd of extras in acting to shout the word "rhubarb" repeatedly and out of step with each other, to cause the effect of general hubbub. As a result, the word "rhubarb" sometimes is used to mean "length of superfluous text in speaking or writing", or a general term to refer to irrelevant chatter by chorus or extra actors.

Possibly from this usage, possibly from a variant on "rube", or perhaps some of both, the word also denotes a loud argument. The term has been most commonly used in baseball.

In the 1989 film Batman, The Joker (Jack Nicholson) tells Bruce Wayne (Michael Keaton) to "never rub another man's rhubarb". The term was used as a threat to Bruce Wayne warning him to leave both men's love interest Vicki Vale (Kim Basinger) alone.

The phrase "out in the rhubarb patch" can be used to describe a place being in the far reaches of an area. Rhubarb is usually grown at the outer edges of the garden in the less desirable and unkept area.

"Donkey Rhubarb" is used as a term when referring to the drug-oriented uses of cannabis. For example, the word takes the place of words such as "weed" or "pot" in some places in Canada.

Rhubarb, specifically in the form of the fictitious product "Be-Bop-A-Re-Bop Rhubarb Pie", is frequently mentioned in "A Prairie Home Companion". In the 2006 film adaptation of the program, the pies are not mentioned, but rhubarb itself is, including an explanation of the source of the name.

[source: Wikipedia]