Heck, even if Biebers Lawyer wants to stipulate that Bieber accidentally said US, I bet that they can argue that his being under the influence could contribute to a mistake in admission or something.
Bieber might have totally correctly claimed that he is an american. USAians, Canadians, Mexicans, Brazilians, they are all american. Bieber would be north american. Not his problem if the police officer doesn't know that there are two countries in north america.
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The little **** (thanks rdowns for his new name) isn't 21 so I'm pretty sure any BAC over 0.0 is illegal.
Since I was born and raised in a country where an 18 year old is a full adult, and I was allowed to drink any amount of alcohol I wanted when I was 18 (with full responsibility for any consequences), I somehow can't get excited about Bieber drinking at the age of 19.