I was flying to Yakima yesterday, talking to Seattle Center, an air-traffic control facility that covers most of the northwest United States. Seattle Center is responsible for the airspace that's not around big airports; you talk to Seattle Approach when you're coming in to SeaTac, you talk to Portland Approach when you're coming in to Portland International, etc., and you talk to Seattle Center once you're outside of Approach's airspace.
As a small plane flying under Visual rules (the big planes are all flying under much more restrictive and communication-required Instrument rules), I talk to ATC mostly so they know where I am in case of potential conflicts, and for the reassurance that someone is paying attention to me if anything goes wrong.
Normally, on the radio with Center, it's all business all the time. You get a lot of exchanges like this, where this is the entire conversation:
Controller: United 123, turn left heading zero-five-zero.
United 123: Left to zero-five-zero, United 123.
It's normal to get a long string of these instructions, so you get used to the rhythm of the language.
Controller: Alaska 234, climb and maintain fifteen thousand, one-five thousand.
Alaska 234: Climb to fifteen, one-five, Alaska 234.
Controller: UPS 987 heavy, turn left heading one-two-zero for traffic.
UPS 987 heavy: Roger, left turn to one-twenty, UPS 987 heavy.
Controller: Cessna 456-Tango, contact Seattle Approach, one-one-niner point two. Good day.
Cessna 456T: Nineteen-two for 456-Tango, good day.
Airplanes are handed off to different controllers by zone, so when you cross from one zone into another, you get passed off to that zone's controller. When you switch frequencies, you check in with the new controller, so they know you're on frequency and talking to them:
Cessna 456T: Seattle Approach, Cessna 456-Tango with you, ten-thousand-five-hundred, VFR.
Controller: Cessna 456-Tango, roger.
So when something unusual happens, it sticks out just because it disrupts the flow. Thus the following incident, which happened more or less like this (details changed because I can't remember them), sticks in my memory:
Santos 123: Seattle Center, Santos 123 with you, ten-thousand.
Controller: Aircraft calling Center, say again the callsign?
Santos 123: It's Santos 123, that's Spanish for "underpaid."
Unexpectedly long pause
Controller: [barely contained laughter] Ok, Santos 123, maintain ten-thousand, expect lower in one-zero miles.
I suspect, unfortunately, that you had to be there, but it was a good joke.