What is the meaning of the phrase you are a caution?

Answer 1

The phrase "you're a caution" is a colloquialism (informal phrase), and may have different meanings in different parts of the country.

In my experience it usually means you are funny, clever or different in an interestingly way. It's usually used in a positive, complimentary or fun way.

Answer 2

1) A 'character,' an eccentric, a 'difficult' person, sometimes extended as a caution to snakes. 2) Anything staggering or alarming [i.e. one with whom caution must be exerted]. (Cassell's Dictionary of Slang)