Green’s Dictionary of Slang

back-to-front, backwards.

1981		B. Downey Uncle Sam Must be Losing the War 100: ‘That’s the way the Corps works,’ Davis groused, ‘backassward.’.
1990		S. Morgan Homeboy 4: I was born backasswards.
2002		S. Jones Pop Music and the Press 248: But I came to Joyce and all the others backassward.
2013		Guardian 9 Dec. 🌐 That, certainly, plus he has it bass ackwards anyway.