Over the past several years, I've worked hard to perfect my Argentine Spanish. I've learned a fair bit of the lingo and tried my best to adopt the cadence and accent of an Argentine from the province of Buenos Aires (after all, there are many accents in Argentina!). I'm far from perfect, but I usually manage to fool native speakers for at least a minute or two. Even once they've realized I'm foreign (usually because of those pesky American r's), they have a hard time believing that I learned to speak Spanish as well as I do without having been born in Argentina or having Argentine parents.
This hilarious video (it's subtitled, by the way, so even you non-Spanish speakers can enjoy it) by an American reenacts a typical first-time exchange with an Argentine. It cracked me up because I swear I've had the exact same conversation with people here.
Can you fool a native speaker with your accent?