Green’s Dictionary of Slang

(US) energetic, spirited, amusing.

1969		Guardian 1 Mar. 🌐 The Minister wore in his lapel [...] a zappy coloured badge of the ‘Cocoa makes you sterile’ type.
1973		Listener 13 Sept. 352: The style is De Vries’s customarily zappy, pun-a-minute stuff.
1999		Guardian 6 Dec. 18: Their zappy professional partnership led to marriage.