Green’s Dictionary of Slang

toby n.1

[Toby, dimin. of proper name Tobias; thus euph.]

1. [late 17C–mid-19C] the posterior, the buttocks.

2. [late 17C–1920s] a woman’s genitals.

In phrases

tickle someone’s toby (v.)

[early 19C] to fawn on, to toady to.

toby-tickle (v.)

to have sexual intercourse.