Joe Who means: Nickname for Joe Clark (Charles Joseph Clark, born 1939), Canadian businessman, writer and politician who served as the 16th prime minister of Canada from 1979 to 1980.. It is mainly Canadian English and may not be understood outside that context. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.