A person who is acting insane, bizarre or highly unusual or the result of when a person with mental illness decides they are 'better' and goes off their meds.
My mom was acting like a complete whackadoodle yesterday. What a surprise, she went off her meds AGAIN!
A paranoid conspiracy nut, usually on the right wing of the political spectrum.
Those whackadoodles at the tea party rally were convinced that extending unemployment benefits was a plot perpetrated by the socialist puppetmasters of the U.N.
-A person not of sound mind or body.
-My boss went all whackadoodle on me today, when I reminded him I was leaving early.