I (white boy) visited India in the early '90s and brought back a bunch of rolls of half-Rupee coins as souvenirs. Turns out they were the exact same weight and diameter as US quarters (even down to the number of ridges, which makes me suspect India bought a bunch of used US minting machines to make them), so I started using them at laundromats. The exchange rate at the time was 35 Rs to the dollar, so a load in the US that normally cost $1 was costing me less than 6 cents. I do feel bad for the harassment that actual Indian customers probably ended up receiving, although possibly the owners never noticed or cared.