The overloading of the shi sound in mandarin approaches absurd levels.

I've always liked:

四 是 四 ， 十 是 十 ， 十 四 是 十 四 ， 四 十 是 四 十 ， 四 十 四 只 石 狮 子 是 死 的 sì shì sì shí shì shí shí sì shì shí sì sì shí shì sì shí sì shí sì zhī shí shī zǐ shì sǐ de. Translation: 4 is 4, 10 is 10, 14 is 14, 40 is 40, 44 small stones are dead

Then get a southerner with say a Sichuan or yunnan accent to say this (in mandarin). They cannot properly pronounce shi (they say it like si). The above just sounds like an angry bee. Given that shi and si is used a lot this becomes a real pain for a non native speaker.

Makes this tough when you're buying something that is 44 rmb and you cant tell whether they said "is 14" or "44" or what.