厄鬼吃豆腐 direct translation: to pursuade the foreigner to eat tofu. Tofu is very cheap, so the merchant can make more profit. This expression imply that the foreigners would not know the value of the tofu, they will be pursuaded to pay for the higher price. This expression also mean that you are very easy to be fooled.

我們香港人叫外国人係鬼呀﹐而不是真的有鬼比你呃。 In the 60s and 70s, the people in Hong Kong call those brown hairs and/or blue eyes foreigners "GHOST". Because they look different. The man is called 鬼佬, woman is called 鬼婆, girl is called 鬼妹and the boy is called 鬼仔.In general, they are being called ghosts. The HK people thought that they are more intelligence than those ghosts, they always try to create some slangs to insult the foreigners, 鬼 is the insulting word. 厄鬼吃豆腐 is to insult the person with lower IQ, he/she is very easy to be fooled.

it is a Cantonese expression(as HK merchant explained),we use this phase in some colloquial and imformal situation. But it is not an malicious way of insulting someone. It is used between frds means,"hey are you kidding me.don't fool me! I don't believe it!" By the way ...we seldom write it down... so it takes me a few seconds to understand what you are asking;)haha

以前有一个书生（什麽地方的人就有待查证），他的口才非常厉害，而且骗人的功夫毫不含糊。有一晚，有一只鬼到了他的家里，这只鬼已经很久没有吃人了要把他吃掉。但这个书生毫不害怕，就对这只鬼说：“你要吃我啊？我已经很多天没有洗澡了，我的肉又酸又臭，不好吃的。不如你吃我锅里的豆腐吧，豆腐比我的肉嫩多了。”谁知道这只鬼很笨，对他的话信以为真，把豆腐给吃掉。 还说很好吃。第二天，他又把他的经历添油加醋地告诉村里的村民。那些村民就说：“你啊，真是连鬼都让你骗到不吃人，改吃豆腐了。” 到了现代，广州人经常说：“你呃鬼食豆腐啊？”意思就是对你地话极之不信任 lol can you understand? jiejie it is ok I will tell you when we chat