I've heard American voices stand out among the muted conversations in a French bistro. I have been to Holland where a group of German tourists was so loud that the Dutch patrons asked for the room partition to be folded out. I've heard middle eastern people 'yelling' to each other in regular conversations in their back yard. I don't think any one nationality holds this dubious honor.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma