What's The Deal With The Lights?

I was watching the very first episode of "The Walking Dead" with my son tonight.  In it, the two lead characters who are Sheriff Deputies are having a conversation about some differences between men and women.  The one character spent quite a bit of time complaining that his significant other would never shut a light off.  She'd walk in a room and turn on the light.  But then when she would leave the room, she wouldn't bother to shut the light off.  Obviously that is a huge waste of energy, so I get the complaint.  But he makes it sound like she's too stupid to shut the light off.  I don't think it's stupidity, just laziness.  It's kind of like when guys don't bother to put the toilet seat back down.  Guys just can't be bothered.  So it must be that girls can't be bothered to turn off the lights.  However, I find that perception rather odd.  I have never noticed any gender difference in that type of thing.  Most people I know are very good about turning off the lights.  It must be because we're all so money-conscious these days, since the economy went in the toilet.  But historically, I really don't feel like energy conservation (or lack thereof) jumps out as a common stereotype based on gender.  Has anyone out there noticed such a tendency in your life?  I would be interested in getting some comments about what you have experienced.  Thanks!