The Foreigner Card: When to use a bad accent?

I was just browsing through some of my fellow gringo-in-Chile blogs and I read this post by Margaret. It's terrific. She brings up a good point. There are some people who will actually fake a bad accent, or horrible Spanish to get out of a tricky situation. I may have even done it on occasion when walking through a market place with a throng of annoying men pestering me to buy their fruits and vegetables. Generally their English is limited to "boo-ti-fuul gee-rul" so that's not a problem, or they just shout out all the random English words they know like "RabbitBatMonkeyApplePoop" (Thanks to Lydia for bringing that to my attention!)

Now, I take particular offense to people speaking to me in English. It's like they are insulting my Spanish (or German teehehehe). Hello, I didn't go for four years to a crazy liberal arts school and study abroad in three countries for this! So, I might be a tad arrogant, too.

Anyways, all bantering aside, when do you think it's best to fake a bad accent, or fake that you don't know what's going on when you really do?

I would maybe consider doing it to get out of a parking/speeding ticket or for some other such offense. I have once done it to avoid standing in the eternal line of bureaucracy hell that is otherwise known as where you have to go to return crap at a local department store. I simple smiled at the lady with my cutest, most convincing gringa smile, and said "NO.ENTENDER." She huffed off and returned my garment for me. Perfect.

But, is it fair to always play the foreigner card when traveling or living abroad? Have you ever done it in your own city? (I may have also done that once, but I'm not sure I want to brag about it here).