Green’s Dictionary of Slang

(orig. US) a form of address, often implying that the person in question has a higher opinion of themselves than does the audience.

1933		L. Stone Larrikin 12: Blimey! ’ot stuff, ain’t it?
1983		R. Price Breaks 16: Whatta you lookin’ at, hot stuff . . .
1999		Indep. Rev. 28 June 4: Billboard magazine said [...] ‘Both lyrically and vocally, she’s on.’ Hot stuff!