Madness had a song called Pac-a-Mac and sang:
Another website told me:When it rains
Cats and dogs
From my pocket I pick a pac-a-mac.
In modern online shopping catalogs, they are not necessarily so thin, however.The Pacamac was in vogue in the 1960s. The precurser to the cagoule, it consisted of a large sheet of brightly coloured polythene, cut and moulded into the shape of a coat, pliable enough to fold very small so you could keep it handy in your pocket and if it rained you could pull it out, put it on and spend the duration of the shower looking like a Durex Fiesta. The Pacamac had two drawbacks. First, it wasn't waterproof, and second, it made you sweat so much there was no point in wearing it in the first place. The modern equivalent of Pacamac wearers are people who wear transparent plastic raincoats with transparent hoods, obviously with the sole intention of imitating a large packet of crisps.
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