This one goes back a long way and is of Australian origin. There are a variety of definitions for it out there all in a similar vein. Mine goes a bit like this – “Someone who wants to ruin everyone else’s fun”.
Wowsers are the reason why there is only one pub in Neutral Bay and on the upper North Shore (home of the conservatives) there is only one every 5 kms (or 2 or 3 train stops). Wowsers dress in a uniform of suits during the week and some sort of camoflauge on the weekend (probably too scared to leave the house).
Wowsers think the crime rate is soaring, kids are all evil and of course back in their day everything was better. They block development and progress and in the course of making everyone else’s lives hell they continue to think that they have some sort of divine right to do it.
If you’d like to learn more about wowser and other uniquely Australian words and their origins the ANU website is a great resource.