I like Pi, I like Pi 3.14159! Retort: So do I, So do I 3.14159!
3 people start, the first one at the second singing, then the second one retorts. then they both go out to a member of the audience and sing the first line. Then the members of the audience that were sang at sing the retort, and go off and do it to someone else, until everyone is standing and singing.
Geared toward older scouts. this song starts out with three people, and eventually gets everyone involved. You should show everyone what to do before actually doing it