Green’s Dictionary of Slang

(Aus./S.Afr.) of persons or objects, weak, feeble.

1904		Sydney Sportsman (Surry Hills, NSW) 14 Dec. 2/4: [A] pappy ladies’ paper has a par to the effect that his presence of mind [...] saved Her Majesty’s [theatre] from a big blaze.
1934		C.P. Swart Supplement to Pettman 133: Pap, [...] in its adjectival sense ‘soft’, it is steadily gaining ground among English-speaking South Africans and one frequently hears such expressions as: the tennis balls are ‘pap’; the tyres are ‘pap’; I’m feeling ‘pap’ (exhausted).
1975		S. Roberts Outside Life’s Feast 27: His chest hangs like soft tits in his vest. He is pap.
1999		Observer Screen 27 June 20: Let’s be honest, these tuppence ha’penny offerings are pap.