Green’s Dictionary of Slang

1. (US campus) someone or something splendid.

1928

R. Carr Rampant Age 32: Taking a wild ride clear to the city with a buncha Regular Guys! Hot rocks! [Ibid.] 43: Skeeter’ll be hot rocks when he’s a Senior.

2. (US) biscuits.

1936		R.F. Adams Cowboy Lingo 147: ‘Sour-doughs’ were biscuit such as only a cow-camp cook could make; they were also known as ‘dough-gods,’ ‘sinkers,’ or ‘hot rocks’.
1955		Great Bend Trib. (KS) 2 July 3/1: Biscuits [...] go by any other name [...] ‘dough gods’ [...] ‘hot rocks’.

3. (US) esp. of a man, strong sexual desire.

1947–51		W. Motley We Fished All Night 168: I’ve got hot rocks....Let’s get layed [HDAS].
1962		J. Quirk No Red Ribbons (1968) 13: He approved of hell-raising ashore, and he approved of derring-do in the air. He believed that the anti-civilization attitude of his hot rocks directly contributed to his flying ability. [...] ‘I didn’t get the name flying. I’ve got hot rocks.’.

4. (US) as a form of address, usu. ironically.

1950		R. Bissell Stretch on the River 115: Listen, hotrocks,...whadda you think we’re doing out there, playing duck on a rock? [HDAS].
1962		J. Quirk No Red Ribbons (1968) 13: This simple tool’s Hot Rock Bennett.