Years ago, I flew out of Santa Monica (SMO). Primary students quickly learned the controllers were sticklers, especially regarding radio communication. And that's understandable given the high volume of traffic. Early on a Saturday morning, I was holding short, awaiting clearance and monitoring the tower frequency. A student (I checked later) from an area airport was in the pattern.
"Piper One Two Uniform, cleared to land."
"Cleared to land, One Two Unicorn."
[about a minute later]
"One Two Uniform, contact Ground on 121.9."
"Ah okay, 121.9. And, ah, we're One Two UNICORN."
"That's fine, One Two UNICORN. You just go ahead now and contact Ground on 121.9 right away."
[Gales of laughter were heard in the background.]
J. Barry Mitchell