Vegas cab drivers hassling for tips

[peterchi]

On two of my most recent cab rides in Las Vegas, the cab drivers gave me crap about my tips.

One was to the airport. The fare was $11.40, I gave him $20 and asked for $7 back. He looked at me funny, went to get his cash, then said,
"You know it's $11.40, right?"
-"yes... why?"
"Only $1 tip??"
-"No, $1.60... what's wrong with that?"
"Man, you know we work on tips"
-"What? How much do you want?

He continued to be quite aggressive and rude about it, so I insisted on getting $7 back. I did almost give him more, but decided not to due to how he was talking to me.

Then today, I got a taxi from McCarran to the strip. Firstly, he took the route through the tunnel, so my fare ended up being a bit more than if he hadn't. It said $19.80 when I got out, so I gave him $25 and asked for $3 back. Barely 10% which I didn't feel great about, but I wasn't too happy about him having gone the long way.

Then he says,
"You know it's $21.20 right?"
-"No, it said $19.80..."
"No it's $21.20", and then he plays with the ticker and it still says $19.80 until he hits some buttons to make it say $21.20

Then I say,
"Ok, then let me ask you a question. Why did you go through the tunnel?"

He says,
"It's faster that way right now, with all the construction. And time is money in this business."

What. Ever.

I eventually let him give me just $2 back, which clearly neither of us are happy about. I've been told about taxis going through the tunnel, but it's never actually happened to me before.

Questions:
1) Do you guys usually specify not to go through the tunnel when you get in a cab from McCarran?
2) Has anyone else noticed cab drivers getting increasingly aggressive lately? I know my sample size is small, but in like 30 taxi rides in the past couple of years, I've never been hassled about my tips until these two times.

Thanks.