Senior year. Chemistry.
We had an activity. Part of the activity, as usual, was writing the chemical formula of the elements and/or compounds involved. We were paired for the activity. My pair was my close friend, Marianne. In the activity, there was an unpotable water mixed with something. Being the funny person that she is, Marianne said,
What is the chemical formula for unpotable water? H2O-dirty?
Even today I still laugh when I remember that day.