Drop A Bad Habit

Why makes this Joke funny?

This joke plays on the ambiguity of language and the unexpected twist in its structure.
Initially, it sets up an expectation that the speaker stopped an unhealthy habit (drinking), which is a common setup for jokes about self-improvement or health.
However, the punchline subverts this expectation by revealing that what the speaker actually gave up was not drinking, but thinking.
This twist creates humor through its surprise and the absurdity of the idea that one would stop thinking instead of stopping a potentially harmful habit.
It also plays into common comedic themes about avoiding problems or responsibilities in humorous or exaggerated ways.