Green’s Dictionary of Slang

1. intensely, excessively, obsessively.

1905		Lippincott's Mthly Mag. 76 719: We got a fine start and went by the group on the road at a twenty-mile clip, the Duke slapping the nags and yelling like crazy.
1912		A.M. Chase Heart of an Orphan 140: There sat Dolly on her side writing like crazy in her play notebook.
1925		Boys’ Life Dec. 40/3: The Boonville fans were yelling like crazy.
1935		C. Odets Awake and Sing! I i: Work like crazy!
1952		(con. 1948) G. Mandel Flee the Angry Strangers 96: He’s on the dog like a horse, laughing like crazy.
1964		H. Selby Jr Last Exit to Brooklyn 23: We [...] were blasting like crazy and were up so high.
1971		E. Taylor Mrs Palfrey at the Claremont (1982) 35: Who is that old codger there, staring at me like crazy.
1977		C. McFadden Serial 74: They must get crank calls like crazy.
1993		K. Scott Monster (1994) 249: The back of my head [...] was stinging like crazy.
2000		Indep. 9 Feb. 3: He heard the couple fighting ‘like crazy’.
2010		Sun. Times Mag. 19 Dec. 34/1: He was, he says, ‘self-medicating like crazy [...] a total f***ing wreck’.

2. as fast as possible.

1947		‘F. Bonnamy’ Self Portrait of Murder (1951) 75: That old wood burns like crazy.
1972		P. Fordham Inside the Und. 44: We shoved it in like crazy.
1999		Guardian 11 Sept. 2: We’re selling it like crazy.

3. (Aus.) used to negate the previous speaker’s remark.

1964

‘Charles Barrett’ Address: Kings Cross 83: ‘How’s it going? Not good? No work?’ I shook my head. ‘Like crazy, there’s no work’.