'Thongs' has two completely different meanings depending on country. In Australia and New Zealand it means flip-flops — the rubber-soled sandals you wear to the beach. In American and British English it primarily means a style of underwear or swimwear with a narrow back strap. If your Australian-influenced teen says 'I need new thongs for summer' they are talking about beach footwear, not lingerie. Context and accent are the giveaways. Confusing but harmless — many an Australian visitor to the US has caused embarrassment by asking where they can buy 'a cheap pair of thongs'.