The story
Acronym of cracker-ass cracker. Emerged on African-American internet forums in the early 2000s. Originally spelled in uppercase (see CAC), with the lowercase form becoming more popular in the 2010s. The reduplication "cracker-ass cracker" was popularised by stand-up comedian Chris Rock in his 1999 television special Bigger & Blacker.
Etymology from Wiktionary, CC BY-SA 4.0.