look up any word, like fleek:
 
1.
crazy, weirdo, dummy.
that girl is a whacko for dating a guy who is 20 years older than her!
by angel-roh April 04, 2005
 
2.
Something surprising and often of interest. Generally said with a british accent for effect.
"Hey check out this new gadget."
"Oh, whacko."
by Ender April 11, 2004