Green’s Dictionary of Slang

(US) to lie, to flatter.

1954		J. Thompson Swell-Looking Babe 87: Don’t try to horse-shit me.
1967		L. Bruce Essential Lenny Bruce 106: I’m not horseshittin’ you.
2001		(con. 1964–8) J. Ellroy Cold Six Thousand 89: Find her some nonunion backup. Scotty & the Scabs or the Happy Horseshitters — a fixed rate and a cut.
2004		N. Tarrant Dissolution 306: Don’t horseshit me, Sean, not now. No time for it. Just straight answers between the two of us.