From The Jargon File (version 4.4.7, 29 Dec 2003):
whacker
n.
[University of Maryland: from hacker]
1. A person, similar to a hacker, who enjoys exploring the details of
programmable systems and how to stretch their capabilities. Whereas a
hacker tends to produce great hacks, a whacker only ends up whacking the
system or program in question. Whackers are often quite egotistical and
eager to claim wizard status, regardless of the views of their peers.
2. A person who is good at programming quickly, though rather poorly and
ineptly.