Now - about "rationalizational." Tammet notes that the English language has an almost undefinable number of possible words because of the combinatorial possibilites generated through the use of prefixes and suffixes. As an example he offers the noun "ration," originally defined as "reasoning." When the suffix "-al" is added, the noun becomes the adjective "rational." Now add the suffix "-ize" to the adjective, and you create the verb "rationalize." Once again, add the suffix "-tion" and you convert the verb back to a noun: "rationalization." The triple-suffixed "rationalization" is the endpoint for conventional English, but in principle the process could go on forever.
The next step would be to add "-al" again to create the adjective "rationalizational." Tammet notes that even though this is not a word, many people have logically and unintentionally "created" it as a neologism to convey a desired meaning, and Googling the word yields 161 hits. (TYWKIWDBI may offer the 162nd after this blog post gets logged by Google.)