Did you hear the joke about the broken glass?

This joke is a play on the phrase “not all it’s cracked up to be,” which means something is not as good as people have claimed it to be. The humor comes from the literal use of the word “cracked” in relation to glass. When glass is broken, it cracks, so the joke is making a pun by combining the literal cracking of glass with the idiomatic expression. It’s a simple wordplay joke that relies on the double meaning of “cracked” – both as a physical break in the glass and as part of the idiom describing disappointment.