Crowds on Demand, as the name suggests, is a company that will organize a crowd for you, on demand.
The two main scenarios that require this service are: 1) You're an
aspiring celebrity who wants to make it seem like people give a shit
about you, so you hire some fake fans; or 2) you believe in a cause and
want to make it seem like people give a shit about it, so you hire some
fake protesters.