Justin Timberlake pleads not guilty to drunk driving charge

In most US states, you don't need to be drunk to be arrested for impaired driving. He claims he wasn't drunk, but unless he's been tested as he drinks and learns how much he can actually drink AND not be over the legal limit, he doesn't really know.

The amount of alcohol, how well rested he was, and a few other factors go into "impairment". He was swerving on the road, so he was at a minimum distracted and had 1 drink. Who's to say that the bartender didn't make the drink extra strong - I've seen that a few times myself. A bartender would put double the alcohol into some drinks for "friends". Also, people who drink often usually downplay how much they've had.

I friend lost his license due to being found guilty of drunk driving. He'd had 2 drinks in 2 hours and said he had a very slight buzz, but wasn't impaired at all. The test showed him as drunk.

In short, he's probably guilty. He should have insisted on a blood test, not a roadside breath test. Usually that would take 60-120 minutes, so more alcohol would be metabolized. The only people likely to refuse a blood test are also narcotics users. In NY, it is allowed to refuse all tests, but that will lead to a 1 year suspended license. For Timberlake, that probably would have been a better option, if he uses narcotics.