A Wikiwacko (also Wikipath and Wikibum, the latter of which is used to indicate the same condition to a smaller degree) is usually a person subjected to so much Wikistress that they snap and discontinue all sane forms of wiki editing.
This condition is invariably characterised by incivility usually accompanied by bouts of vandalism and trolling.
A namespace shift usually accompanies this condition: overstressed users often focus their destructive energies on a small set of pages. They may only edit articles in the main namespace, completely ignoring talk pages — or they may focus on the talk, where incivility will not be reverted as quickly, if at all. (The remnants of past explosions can be easily located by Wikiarchaeologists.) Alternately, users who snap may go off like a shotgun, editing any and all pages they can get their hands on. For users who were previously solid contributors, such "shotgun blasts" are the hardest to clean up after.
If you think you are getting close to going off like a shotgun, then please, please take a Wikivacation! Read the Wikistress page — some of its suggestions have helped this author a time or two.