Missing 13th Amendment
The "Missing 13th Amendment" is not a reference to the 13th Amendment actually in the Constitution but rather is a false concept within the sovereign citizen movement that claims that there is a missing amendment (the ratification of which was covered up by a conspiracy) that prevents anyone with a title of nobility from being a citizen. Sovereign citizens twist the meaning of this in order to attack lawyers, arguing that a lawyer's "esquire" title prevents them from being citizens and therefore makes them invalid. The amendment they refer to was actually passed by Congress in the early 1800s but never was ratified by the requisite number of states.