Most popular association is that of Monopoly Money, used in the game Monopoly™
2. What ignorant citizens of the USA call foreign currency.
2. US Citizen: "Look at this Monopoly Money! Why can't you have REAL money, like Americans?"
Canadian: "This IS real money."
US Citizen: "I can't understand your stupid accent! SPEAK AMERICAN!"
(Also any country where simple items currently cost 1000's of their currency unit, as this is an indication of past hyperinflation)
Monopoly Money is often spent recklessly because it looks fake, therefore you're not spending "real" money.
New Zealand Dollars
South Africa Rand
Saudi Arabia Riyals