Most people who think they know relate to France's love of frog legs as a delicacy. I can assure you, the only contact I've ever had with the amphibian is the squishy sound they used to make when hiding in the tall grass while I was mowing the lawn.
You have to go back beyond colonial times, in an era (some say hasn't psssed yet) when France and England couldn't stand each other. The sentiment obvisouly traveled to their New World colonies, where their war was valiantly upheld. When a loosing France conceded its America colonies to the King of England, he gave us an incentive - we get to keep our culture, language and laws. The object was to gain our loyalty, which we did give - when the 13 New England colonies revolted and asked our participation, we refused. When they invaded, we turned them back. But that wasn't enough for the English loyalists to tolerate us - we still hated each other. They had the number, and thus the right to bully us.
Now, keeping our culture means our heritage and symbols as well. The most obvious one, if you intend to remember your French ancestry, is the French Royalty emblem, the Fleur de Lys.To a casual observer who knows not of the flower reference, it might very easily look like a frog seen from above. Hence the racial slur, which English colonials took to calling us for a long while.
I for one never shied away from the symbol, nor did the rest of our nation since we made it into our national flag. It doesn't really indicate to us that we look like a green marsh-dwelling amphibian whose voice bears an uncanny resemblance to Jim Henson's. It means that whoever uses the slur has little to no understanding of European history and culture.
To really offend us, use something that is indeed indegenous to us only, as MIcheal Moore did (in the highly underrated and hilarious gem Canadian Bacon) - pea soup-eaters, Poutine-makers, Bonhomme-worshippers. At least those are slurs both offender and offendee can understand. And truly hate each other over.
For anyone curious of this article's title, it refers to a politicaly-charged humourous song of the 70's by Quebec singer Robert Charlebois.