Tip envy

So I drive two Medical residents to the airport and after we get there and I get their luggage out the following exchange occurs:
"Hey man, do you ahve change?"
"Yeah."
"Wow. You're the man with the change," said the same guest that had asked me for change the night before. "Just gimme two back. Is that good? You tell me bud, is three ok?"
"Yes, sir that's perfectly fine, thank you."
Then the other gentleman tips me as well.
"Hmmm," the first man hums, looking over at the second man. "What did you give him?"