My chemistry teacher threw sodium chloride at me.

This joke hinges entirely on a clever bit of wordplay, specifically a homophone. The humor comes from the punchline "That's a salt," which sounds exactly like "that's assault." The setup provides the perfect scientific context, as sodium chloride is the chemical name for common table salt. It's a classic example of a pun, where a single word or phrase is used with two different meanings, creating a humorous twist.

The real-world context here is straightforward chemistry. Sodium chloride (NaCl) is one of the most fundamental and widely known chemical compounds, essential for life and a staple in kitchens worldwide. The joke takes this everyday scientific fact and playfully twists it into a legal or aggressive context, making light of the idea of a teacher throwing chemicals, even if it's just harmless table salt. It’s a quick, clean joke that relies on the listener's basic understanding of both chemistry and common English phrases to land its punch.