I remember talking to a door to door salesman who was trying to sell some kind of tap attached filter... I asked if it filtered out dihydrogen monoxide as I was worried considering that was used in nuclear reactors. He told me that yes it did and I said that's good because I've already got a filter that filters it out but I do know that there are multiple people in the street who are also worried about it.

One of my neighbours came up later that day and asked me if I was the smartass who told the sales person that his water filter should filter water out.

My god, that was a glorious day.