They're both only three fifths of a person
An idle worshiper.
You: You can tuna piano but you can't piano a tuna! Person getting told joke: What about the jar of glue? You: I knew you'd get stuck there
Inert gas.
They never carry their own weight.
Canoes tip.
His upper lip.
Three-fifths as many seems like a generous offer.
Three Fifths