Green’s Dictionary of Slang

1. foolish, soft.

1873		Sl. Dict. 343: Yappy soft, foolish; mostly applied to an over-generous person, from the fact that it originally meant one who paid for everything.
1880		W. Hooe Sharping London 36: Yappy, simple, foolish.
1881		Newcastle Courant 2 Dec. 6/6: He had no eyes at all when he passed us, yer yappy cull.
1902		Ade Breaking Into Society (1904) 38: It was argued that one so Yappy would have to be correspondingly Honest.
1938		W. Winchell On Broadway 19 Mar. [synd. col.] Whoever said I advised Lupe to sue for libel is nuts. Who starts such yappy rumors, anyway?

2. (Ulster) thin, hungry-looking [one’s mouth is fig. open with hunger].

1997

Share Slanguage.

3. (orig. US) noisy, talkative; thus yappiness n., verbosity.

1931		Ade Old-Time Saloon 162: The boys and girls now in their late teens are more sophisticated and better specimens of physical development and more sensibly attired and better-groomed than the yappy youngsters of the eighties and nineties.
1938		W. Winchell ‘On Broadway’ 8 Aug. [synd. col.] It was too bad that the tribute to irving berlin [...] was marred by the nervousness and yappiness of filmdom’s Best Program Spiler.
1942		W. Winchell 19 Apr. [synd. col.] Wonder how yappy newspaper editors who defended [...] Hoffman feel about him now?
1999		Guardian 20 July 21: The yappy rapper who [...] calls himself Master D.
2000		F.X. Toole Rope Burns 9: Ali was yappy before, during, and after a fight.

4. (US campus) over-generous.

1997–2000

Da Bomb 🌐 31: Yappy: Over-generous.