Every so often, I post about how much background information can be required to make sense of what’s going on in a cartoon (and then to see why it’s funny); see, for example, “Bizarro followup” of 8/29. Now, through several Facebook friends, this wonderful New Yorker cartoon by Nick Downes:
First, you need to recognize the two figures at the door as clowns — sociocultural knowledge, but very widespread, so that’s not particularly challenging.
The man at the desk is telling someone on the phone that “they” (that is, we calculate, the clowns) have arrived, presupposing some previous discussion about the clowns. But why does he say “Don’t bother”?
To work that out, you need to supply a very particular bit of sociocultural knowledge. You need to know a specific song, or at least its title.