“I am.” is reportedly the shortest sentence in the English language. Could it be that “I do.” is the longest sentence?

"I am." is reportedly the shortest sentence in the English language. Could it be that "I do." is the longest sentence? - George Carlin

Here is a joke by comedian George Carlin. A lot of humor comes out of a deeper understanding of a language. Sometimes jokes subvert our expectations (do the opposite of what we expect). Sometimes jokes present a different viewpoint than we are expecting. Here, George Carlin uses a homonym to create joke.

'Sentence' is used in two different ways. In the first use, Carlin is explaining that "I am." is the shortest way to write a grammatically correct sentence. So, in this sense he is talking about the collection of words. Interestingly, "i" is considered the longest poem. I will link a picture in the comments to show you the poem. You can decide if it is poetry.
The second meaning of 'sentence' is a length of time that someone must stay in prison. It is a punishment. Since, "I do." is most commonly used during weddings, he is saying that getting married is the longest punishment.