Green’s Dictionary of Slang

boo-boo n.7

[abbr. SE buttocks]

(US) the buttocks, the posterior.

[US]J. Ridley Everybody Smokes in Hell 175: Kiss my boo-boo and make it better.
[US]Simon & Burns ‘Ebb Tide’ Wire ser. 2 ep. 1 [TV script] Let me give your little boo-boo a kiss.