Green’s Dictionary of Slang

holy friar n.

a liar.

1890		Sporting Times 22 Mar. 1/2: The way to win I give in verse — If not I’m a ‘Holy Friar;’ / Put a pony on Aperse, / Place a monkey on Sweetbriar.
1900		‘Doss Chiderdoss’ ‘In Vino Veritas’ Sporting Times 30 June 1/4: I cracked the old wheeze — late at biz — / I’m a rare Holy Friar when sober!
1922		Joyce Ulysses 405: There’s a great big holy friar.
1932		‘P.P.’ Rhy. Sl.
a.1945		L. Payne private coll. n.p.: Liar Holy Friar.
1960		J. Franklyn Dict. of Rhy. Sl.
1969		S.T. Kendall Up the Frog.
1971		J. Jones Rhy. Cockney Sl.
1980		(con. 1930s) Barltrop & Wolveridge Muvver Tongue 31: You’re a holy friar.