a wen/wenny is a girl from the school wenona who is acting as she stereotypically would. she is trying hard, acting like a grom and thinking she is top shit. wens are super annoying.
Originated in Hungry Jacks @ Hornsby in SYDNEY where we would get quite a few patients from the mental hospital. One day one of the crew was trying to point a particular patient out to the rest of us and she was going to say "when" when he came in. It grew from there.
Also know as a Hornsby Grinner, 'cos they are always smiling.