It's well worth checking out the video of Harry Connick Jr messing with an audience by sneaking an extra beat into a piece, thus taking the clapping audience from 1/3 to 2/4.
Without watching the video, it could be reference to the annoying habit non-musical crowds have of clapping on the wrong beats (1 and 3), ruining the feel of a song.
"everybody's clapping on the one and the three"
is a line from the Jason Isbell song The Last of My Kind
https://www.youtube.com/watch?v=N1HqfDQezy0
Anyone know if this is a reference to particular musical traditions where the emphasis is on 1,3 and those where 2,4 are the beat?
thanks