some co-workers and I were talking about this the other day.

A few that seemed to resonate with almost everyone:

-Leaving lights on (including interior car lights)
-Leaving water running
-Leaving doors open (either to the outside or the fridge)
-Overfilling the bath tub (and/or using too much soap/shampoo, i.e., the bubble bath on steroids)
-Taking excessively long showers (usually, only a teenager issue)
-Overusing toilet paper
-Opening up a new package/can of something before an old package/can of the exact same is completely consumed
-Pouring themselves a huge bowl of cereal and then proceeding to eat less than half of it
-Anything having to do with spray whipping cream

When we were growing up, my dad would sometimes threaten to charge us for this type of stuff (and in his case, this included flushing the toilet more than once per use - no, my dad didn't believe in the "courtesy flush" concept).

Any others you've noticed that are not on the list?