Green’s Dictionary of Slang

1. (orig. Scot.) to talk; to talk loudly; to talk nonsense.

1851		‘Epistle from Joe Muggins’s Dog’ in Era (London) 16 Feb. 4/2: You've seen how shaky Grecian haz been lately, spite of ther bonnettin up ov hiz party, and all ther gaffin aboute stakin and kallin to kover.
1874		M. Clarke Term of His Natural Life (1897) 70: ‘Gaffing agin!’ interrupts the giant, angrily. ‘Come to business, carn’t yer?’.
1894		S. Crane in N.Y. Press 9 Dec. in Stallman (1966) 113: ‘What’cher gaffin’ about, hey? Are yeh givin’ me er jolly?’.
1915		Bulletin (Sydney) 5 Aug. 47/2: I goes to May’s place an’ starts gaffin’ to the old ’un erbout things, an’ never mentioning May, ’oping she’ll look in.

2. (US) to tease.

1879

Cincinnati Enquirer 7 Sept. 10/7: Gaff, Taffy--Almost similar to the above [i.e. to kid], but in milder form.

3. (US campus) to insult, to ignore.

1989

P. Munro Sl. U.