Cabbie discount

When I saw my friend Stephen on Friday evening, he said

"I was just thinking about you about fifteen minutes ago."

"How come?"

"I was at Farley's, and a guy walked in and ordered a coffee with the cabbie discount."

"Cabbie discount?"

"Yeah. He got a free coffee and just tipped the guy."

I have never heard of a cabbie discount. I wonder how many other places offer this. I intend to get to the bottom of this.