How about tobacco?
As the weather is slowly getting warmer around here (yup, the increasing K value of the subject is the temperature in Kelvin ) I was reminded of a simple riddle. So;
What is
- black when you buy it
- red when you use it
- gray when you throw it away ?
well if our leader adds a subject "war arguements" (his spelling error, not mine ) then I can add a non-prime topic too I feel