Lojban isn't really a hacking skill, but it's definitely nerdy.
It's a "constructed language" (like Esperanto), but designed to be one capable of precisely expressing complicated concepts, generally making semantic distinctions that are just hand-waved over in English. It's semantics are based on mathematical predicate logic (a typical sentence in Lojban would literally translate as "At some point in the past it was true that the author of this text was eating one or more members of the set of apples"; the idiomatic expression for the English "my wife" in Lojban literally translates as "All members of the set of things which the author of this text is married to, which has one member"; you get the idea).
Particularly delightful features of the language including having sixteen names for digits, so you can pronounce hexadecimal numbers easily, and expression "emotion"/"attitude" by the use of special "attitude marker words", rather than subtle variations in wording or tone of voice. These let you easily put widely varying, yet terrifyingly precise, attitudes on different parts of a sentence; you might say "John is going to see Sarah", while expression righteous indignation about the going, confused helplessness about John, and a mixture of lust and decreasing respect for Sarah, for instance. Lojban poetry can get quite involved.
For more information, see .