The number system is a great policy that only government clerks and very lucky retail staff can still carry out due to insane lineups of snitty, impatient people with petty requests. On the wall, there is a counter which indicates which customer is being served and clients take numbers from a roll of tickets to wait in queue. If someone cannot wait their turn, the friendly customer service representative will then point to the tickets and say "Please take a number."

In my own daily events, there are many occasions where I'd like to ask someone to please take a number. Like when my jackass neighbour knocks on my door looking for weed every Sunday afternoon or when my super wants to discuss the way his tenants are frustrating him. If you've ever been called by a telemarketer at work, or if your boss asks you to go get their dry cleaning for them on your lunch hour.

The applications of this phrase are infinite, as everyone encounters bullshit that's unique to their own life. I'm sure at more than one point in time that you've wanted to tell someone to fuck off. This is just a polite way to suggest it.