Green’s Dictionary of Slang

shoddy-doo n.

[? corruption of SE how do you do]

(US black) any form of ritual hand-slapping that serves as a greeting or farewell.

[US] ‘Return of Honky-Tonk Bud’ in D. Wepman et al. Life (1976) 69: ‘My dear hip friend,’ the letter began, / ‘Here’s some splow and a big shoddy-doo.’.