Green’s Dictionary of Slang

(US black) a general term of abuse, lit. ‘stinking anus’; also attrib.

1969		‘Iceberg Slim’ Mama Black Widow 153: Yu evah cuss me agin, yu stinky butt whore, an Ah’m goin to bus yo brains out.
1981		Indianapolis Star 14 Feb. 34/7: [valentine message] Dear Boo Boo Lips I love you very much! Love, Stinky Butt.
1998		Province (Vancouver, BC) 1 Sept. 37/3: ‘You’re a big stinky butt’.
2000		Sth. Florida Sun Sentinel (Fort Lauderdale, FL) 27 Dec. 81/1: ‘Stinky butt, I call everyone stinky butt. “What’s up stinky butt”’.
2008		Great Falls Trib. (MT) 1 Aug. 26/1: She uses naughty words like [...] stinky butt, poopoo head.
2016		Battle Creek Enquirer (MI) 28 Feb. A5/2: If calling me a ‘stinky butt’ counts as cursing me?