He came to the attention of police when “a state trooper spotted him driving with his right-side wheels on the shoulder of the road“.
People, this is the drifting behavior so often exhibited by drunk or distracted drivers that so often kills or injures bicyclists during so-called “motorist overtaking” errors.

You can read his ridiculous statements made per the police report; The suggestion is he was fishing for legislative immunity, or at least looking for special treatment to wriggle out of his crime (he “handed the trooper his vehicle registration along with a copy of his House of Representatives identification card.”), and as that apparently wasn’t working, moved on to outright threatening the officer’s job. Later when informed his driving privileges would be suspended he indicated his wife works for MVD. 

Extract from AZcentral article:

…Arizona Rep. David Cook told one Department of Public Safety trooper, “Do you know what you’re doing, son?” and told another trooper, “You’ll get yours,” during his arrest on suspicion of drunken driving Wednesday night in Mesa, a DPS report says.

When Cook was also notified his driving privileges were suspended, he replied “It’s fine, my wife works at the MVD,” a Department of Public Safety incident report said, adding that Cook’s blood-alcohol content registered nearly twice the legal limit.

Cook, R-Globe, responded to the controversy in a Facebook post Thursday evening. He apologized and said the incident taught him a “valuable lesson” about the risks of drinking on an empty stomach…

…Cook initially claimed he had dropped his cellphone in his vehicle, which caused him to swerve, the report said. But he then refused to step out of the vehicle and said, “Do you know what you’re doing, son? You’re making a mistake,” according to the report.

While the report doesn’t reference Cook invoking legislative immunity, it states he handed the trooper his vehicle registration along with a copy of his House of Representatives identification card.

 

 For what it’s worth, he did later issue a reasonably contrite apology via his facebook page :

David Cook – Arizona State Representative
December 20, 2018 ·
I learned a valuable lesson the hard way last night, so I want to share it with all of you so you can learn from it as well. No lunch, no dinner, and some drinks with friends sounds harmless enough, but get behind the wheel and try to drive home and you’re taking a chance you just shouldn’t take. I’m lucky, because I got pulled over and got a DUI, but there was no accident, no one got hurt, etc. I’ll be paying a real price for it, and its a humiliating experience for sure, but compared to what can happen when someone drinks and drives, the good Lord was looking out for me.
The DPS officers who handled the matter behaved professionally and did their job well. I didn’t request or receive any sort of special treatment as a result of holding office, as it should be. I’ll be facing a judge and very real consequences which I’ll keep you all updated on as they occur.
I apologize to all of you because I hold myself to a higher standard and I’ve let everyone down, friends and family alike. But let’s not let this be a wasted experience. If you’re out, you’ve had drinks, and there is ANY question in your mind as to your state of readiness, call a cab or a friend. Don’t be worrying about Christmas presents in the back seat or anything like that, because those are all really small things compared to the big things. Again, I’m sorry for what I did and I’ll keep you all posted on the process as it moves forward.

What about Legislative Immunity?

The legislature was not in session at the time of the incident; so it couldn’t have applied.

The Cook incident in December 2018 came a few months after Gov. Ducey issued an executive order deeming such violations a “breach of the peace” and as such immunity cannot apply, and directed DPS (Arizona’s state highway police) to process such traffic violations as usual.

..