Why "off his rocker"?
I'm attracted by the argument made here, that it's to do with trams, given that both "off his trolley" and "off his rocker" appear in print around the same time. I also feel the fact that all the early citations are about "going off your rocker" or "being driven off your rocker" - rather than falling/running/getting - suggests it's the same as "going off the rails".
That said, rocker at the time could refer to:
- chairs
- cradles
- rocking horses
- ore agitators
- rocker arms
- part of a coach or car
- Trevelyan's rocker
- a technical term in numerous patents
Both words have continued to be overloaded: growing up, I associated "off your trolley" with shopping carts, and "off your rocker" with rock stars.
Etymonline says:
rocker "a rocking chair," 1852, Amer.Eng., from rock (v.); [...] Slang off (one's) rocker "crazy" first recorded 1897.
So it's someone who's off his rocking chair. The Phrase Finder also has a thread with people speculating about a different origin, but the conclusion is:
The phrase relates to rocking chairs according to "The Dictionary of Cliches" by James Rogers (Ballantine Books, New York, 1985).
This is more speculation than anything, but it's somewhat stereotypical for older people back in the day to be sitting on rocking chairs and just passing the time, right? What if the phrase originally didn't mean to suggest that someone merely is crazy, but also outwardly displaying it? A crazy person might feel the urge to get out of their chair, run around and act mad, whereas a more mild mannered one would just quietly rock back and forth and not cause a scene.
The best answer I found:
A more interesting topic than first meets the eye!! The phrase first came to light around 1896, and there are 2 schools of thought as to its original reference and meaning:
School one: The "rocker" was the metal strip which held the long metal arms of electric trolleys onto their track. I remember Halifax in the early 1960s still had them - pretty comical when the conductor had to get off in all kinds of weather to manoever the arm back onto its "rocker"!! Here's a quotation from the first source below: "......the first appearance in print of OFF ONE’S TROLLEY in 1896 (see quote below) was followed less than one year later in 1897 (see quote above) by OFF ONE’S ROCKER. This, and the fact that electric trolleys were ‘off’ and running in the 1890s would seem to indicate that we might have more than just a coincidence here. And it strikes me that falling ‘asleep’ in one’s rocking chair is a much more likely event than ‘falling off one’s rocking chair’ – an occurrence seemingly too rare to warrant having an expression named after it – or the even rarer occurrence of somehow being ‘off the rocker’ on one’s rocking chair (whatever that might mean – it’s hard to visualize). On the other hand, even by the 1940s when I would pass three different trolley lines on my mile or so walk to my elementary school every day (yes, kids actually walked to school in those prehistoric times), I often saw men working on a stalled trolley trying to get that overhead, spring-loaded pole, back onto the power line where it belonged – it had gone OFF ITS ROCKER. "
School two (referred to above also): " Originally the phrase was specifically about what we'd now call "mood swings." Now it means "to be crazy," but it used to connote a "normal" person who periodically, and unexpectedly, goes crazy.
"Aw, he's just off his rocker-- it'll pass."
Just imagine the kind of person you'd expect to find "on a rocker." An elderly person, the stodgy old grandma or grandpa most every household has in residence (the expression dates from 1897, before nursing homes were so acceptable). Most of the time they just sit and rock, hands folded, muttering quietly. But every now and then a sudden agitation overcomes old Uncle Nancy, he jumps up and cavorts around the house. Or runs off to the wars with his WWII [actually, WWI] Home Guard helmet on-- "out of uniform" so to speak, like Hyacinth Bucket's old dad. [from the hilarious British sit-come "Keeping up appearances" - still re-run on some USA tele channels!]" - from source 2 below.
Source(s):
http://www.wordwizard.com/phpbb3/viewtopic.php?f=7&t=18057
http://forum.wordreference.com/showthread.php?t=96503
From: http://answers.yahoo.com/question/index?qid=20100831080317AAbDNVw
'Chambers Slang Dictionary’ confirms the rocking chair origin. It also gives this further definition of its use since the 1950s: in figurative use, acting excessively (though not necessarily madly)
The OED’s earliest citation is dated 1890.