The original image was written in traditional characters. Here’s a simplified Chinese transcript:
Don’t feel bad if you don’t get it at first. Some native speakers even take a second to figure out what happened.
This is a case of syntactic ambiguity. You can interpret the first statement in two ways, and it’s all because the verb 教, meaning “to teach,” can take two objects: who is being taught (what we think of as a “indirect object” in English) and what is being taught (what we think of as a “direct object” in English).
The other key is that in Chinese, 没有用的东西 (literally, “useless things”) can also refer to people.
So the joke is that when the student says “everything you teach is useless,” the teacher flips it around and interprets it as “everyone you teach is useless.” Then the teacher pretends to take the high road and says, “I won’t let you talk about yourself that way.”
This is definitely a tricky one, and you’re not likely to be able to appreciate it if you’re not at least the intermediate level. So forgive me for not providing pinyin and translations for everything.
Like many jokes, this joke relies on ambiguity. Understanding the different sentences requires some understanding of semantic ambiguity, syntactic ambiguity, and lexical ambiguity.
Here’s what’s going on:
谁都看不上 can be interpreted as either “doesn’t like anyone” or “isn’t liked by anyone.” You’re not normally going to see both meanings used in one sentence!
This is a parsing issue, and revolves around the word 叫做 being a synonym for 叫: “叫做 爱” (“to be called love”) vs. “叫 做爱” (“to be called making love”). In spoken Chinese, you would definitely pause to verbally insert the “space” that I have typed above.
So 一个人 can be interpreted as both “a person” and “[to be] alone.”
You can’t really praise Chinese for having ambiguity; every language does. And what one human mind can encode, another can decode (native speaker or not!).