Green’s Dictionary of Slang

1. Roman Catholic.

1689		‘King William’s Birthday’ in Ebsworth Bagford Ballads (1878) I 417: For to butcher those craw-thumping dogs, / Our king would not lose his complexion.
1829		London Standard 8 Sept. 1/5: The Craw-thumping clan will triumph o’er the land.
1986		(con. 1930s) P. O’Farrell Tell me, Sean O’Farrell 57: I always had a special soft-spot for Our Lady. I never believed in the ‘craw-thumping’ religion, however.

2. overly religious.

1918		G.E. Griffin ‘Me Bunkie and I’ Ballads of the Regiment 16: Tim Fagin [...] Called Bunkie a ‘psalm-singin’, craw-thumpin’ pup.’.
1925		S. O’Casey Juno and the Paycock Act I: Well, let him give his job to wan of his hymn-singin’, prayer-spoutin’, craw-thumpin’ Confraternity men!
1952		B. MacMahon Children of the Rainbow 230: What’re you pratin’ about, you craw-thumpin’ get?
1969		P. Boyle All Looks Yellow to the Jaundiced Eye 39: You mean that from now on we’re to go round together like a couple of craw-thumping penitents?