xkcd.WTF!?

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Palindrome

I hope that somewhere in the world, "Panamax" is the last option on a "size" drop-down menu on a sex toy site.

Explanation

A palindrome is a word, phrase, or sentence that reads the same whether you read forwards or backwards, like race car. Usually, capitalization, spacing, and punctuation are ignored. This comic is based on the famous palindrome: "A Man, A Plan, A Canal: Panama", devised by Leigh Mercer, which references the construction of the Panama Canal and is the first mentioned on the Wikipedia page for palindromes at the time this comic was released. Megan recites a much longer palindrome for Cueball. This palindrome is based on the original, posted in a forum thread more than three years prior to the release of this comic. Randall's is much less logical and manages to refer to "anal Panama". Notably, in the original version, there was an additional comma before the word "tables", making it a separate item in the list from "God's 'Nam". Due to its list-like structure, the Panama palindrome is easily extensible by adding additional noun phrases, and some of these extensions lay claim to being "The Longest Palindrome Ever".

The title text references the maximum size of ships that can fit through the Panama Canal, which is Panamax. Randall would really enjoy if this was the last option (i.e. biggest size) on a drop-down menu on a sex toy site. For instance such a site could have a banner saying; "If you have a Panama Anus, then try our Panamax Butt plug".

The original palindrome is as follows:

A man, a plan, a God's 'Nam tables, nitrate, tar, tinsel, Batman's dog: Anal Panama.

Reversing the sentence creates the palindrome, which reads the same:

amanaP lanA :god s'namtaB ,lesnit ,rat ,etartin ,selbat maN' s'doG a ,nalp a ,nam A

The same sentence without spaces or other punctuation is easier to read both ways:

amanaplanagodsnamtablesnitratetartinselbatmansdoganalpanama

The meaning of the sentence isn't immediately clear. It doesn't appear to be something created by Randall. The original palindrome was a list of elements that led to the choice of Panama: a man had a plan to make a canal, so he chose Panama. This new palindrome follows a similar list-like structure: a man had a plan to use the Vietnam War, nitrate, tar, and tinsel (possibly implying some kind of explosive involving Christmas decorations) and finally added Batman's dog, resulting in "Anal Panama". The words "Man", "Plan", and "Panama" are from the original palindrome. The rest of the original sentence means:

God's 'Nam
'Nam is here short for Vietnam; God's 'Nam would refer to a Quagmire of God's creation. (The Quagmire is a figurative name of the Vietnam War).
Tables
This can either mean a piece of furniture or a data table.
Nitrate
A polyatomic ion with the molecular formula NO3 that are mainly produced for use as fertilizers in agriculture. But as an oxidizing agents it can be used to create explosives where the rapid oxidation of carbon compounds liberates large volumes of gases. Given the end of the sentence it could also be a reference to Amyl nitrite, for which notable side effects includes "relaxation of involuntary muscles, especially the blood vessel walls and the internal and external anal sphincter."
Tar
Tar is a black mixture of hydrocarbons and free carbon. Originally referred primarily to a substance derived from the wood and roots of pine. But it has also been used in other contexts. For instance naturally occurring "tar pits", actually contain asphalt rather than tar.
Tinsel
Tinsel, is a type of decorative material that mimics the effect of ice, consisting of thin strips of sparkling material attached to a thread. When in long narrow strips not attached to thread, it is called "lametta", and emulates icicles. It was originally a metallic garland for Christmas decoration. The modern production of tinsel typically involves plastic, and is used particularly to decorate Christmas trees.
Batman's dog
Ace the Bat-Hound was the canine crime-fighting partner of Batman and Robin in DC Comics of the 1950s and 1960s.
Anal
It relates to anus. Searching for "Anal Panama" will return links to pages with porn. This is because the most used form of Anal is in regard to Anal Sex which is often used in porn. (It is not long since another xkcd comic referred directly to porn - see 1629: Tools).

In comic 1608: Hoverboard, there is a reference to the palindrome and the Panama Canal with the song that Cueball sings at the ruin to the right. The first four lines of the song is the same as in the original palindrome but with the "A " changed out with Spider-, and then also Spider in front of Panama:

Cueball singing:
Spider-man
Spider-plan
Spider-canal
Spider-Panama
Gates let in
Spider boats
Flood the locks
Spiders float
Look out!
Spiders in both oceans.