Green’s Dictionary of Slang

lay it on v.

1. in senses of communication.

(a) to charge excessively.

(b) [mid-19C+] to exaggerate; to make an excessive fuss.

(c) [1910s+] (orig. US) to criticize, to berate.

(d) [1930s–70s] (US black) to seek a verbal or physical confrontation, to hit.

(e) [1950s+] to inform, to pass on information.

2. [1930s+] (US) to act or work efficiently or energetically.

3. [1970s] (US black) to slap someone’s hand in greeting.