What's the meaning of the phrase 'Bass-ackwards'?
Literally, ass-ackwards means turned so that the back becomes the front. In common usage it is used to refer to things that are chaotic and muddled. It is usually used humorously and is a Spooneristic variant of 'ass-backwards'.
What's the origin of the phrase 'Bass-ackwards'?
This expression is unusual in that, although it seems clear that it is a jokey variant of 'ass-backwards', it actually predates that phrase by a good fifty years.
It is certainly American in origin - the word 'ass' isn't used to mean rear in most other English-speaking countries.
It may be that the explicit use of 'ass' in 'ass-backwards' was the reason that the coy 'bass-ackwards' was initially preferred.
Oddly, 'ass-backwards', although it alludes to things being wrong and muddled, is (the last time I looked) the usual positioning. It shares that strangeness with 'head over heels', which is also the normal way of things.
The earliest example that I can find in print is from the Kansas newspaper the Eureka Sentinel, July 1878:
A traveling gymnast gave a public exhibition on Main St. last Thursday evening. His contortions and double somersaults "bass backwards" was hard to beat.
The earliest example that I can find of 'ass-backwards' is 1934.
See also: 'inside out'.