Tap dancing is what people do when they are absolutely bursting for a piss, to the point of not knowing whether they will be able to prevent wetting their pants. People who are tap dancing jump about on the spot, and then start
Jigging up and down and waving hands and moving back and forth
all help to prevent an embarrasing gush of piss flooding out.
Ohhh maaan I cant get on the bus if it comes now, I been tap dancing for ten minutes and it wont go away.