From AMLopedia
I'm a snowman too! was a catchphrase that Adam spawned when he was a sophomore in high school (2002). Washington Mutual had little butterknives with ceramic snowmen on the handle, and Adam was pretending that they established their own civilization. Then a regular knife with no snowman wanted to join the civilization. The snowmen didn't want him and the regular knife said, "but i'm a snowman too." He told Liam and they both continued to say it regularly.
In March 2005, Liam thought of this catchphrase while sitting in his AP Chemistry class, and started making a list of all the AML Catchphrases. This eventually morphed into the AMLopedia.