Green’s Dictionary of Slang

bass-ackward(s) adv.

back-to-front, backwards.

B. Downey Uncle Sam Must be Losing the War 100: ‘That’s the way the Corps works,’ Davis groused, ‘backassward.’.
[US]S. Morgan Homeboy 4: I was born backasswards.
S. Jones Pop Music and the Press 248: But I came to Joyce and all the others backassward.
[UK]Guardian 9 Dec. [Internet] That, certainly, plus he has it bass ackwards anyway.