"Random Breath Test" joke

From the mouth of Aussie comedian King Billy Cokebottle

I was travellin in the outback one day wit my friend Morton, when off in the distance we sees a booze bus (police).

Morton thinks this is great and heads straight for it.

We pulls up and Morton winds his window down and says "Two cans of Emu Export thanks mate!"

The copper looks at me and Morton and says "You must be drunk! Get out of the car and blow into this bag for me."

Morton got out of the car and said "Sorry boss, I can't blow in that. I got a letter from the doc saying I'm asthmatic and I'll pass out if I blow in that."

The cop looks at him and with a bemused look and says "OK. In these cases we require you to give a blood sample."

"Nah nah sorry boss. Can't be doin that. I got a letter from the Red Cross saying I'm a Hemophiliac and I could bleed to death. Sorry boss, can't do that" said Morton.

By now the copper is getting fairly pissed off and finally demands a urine sample for testing.

Morton looks at him and says "Sorry boss, can't do that either."

The copper says "Surely you can't have a letter for that!!! "

"Bloody oath mate." says Morton. "It's from the government. Says that you whites can't take the piss out of us Black Fellers."