I'm the same way & didn't realize there was a watermelon stereotype until a couple of years ago.
I almost think (& this is just from my own experience) that people who have grown up in the South are just not going to see watermelon as anything but a summer fruit - because we all grew up eating it, if that makes sense.
And people that didn't have the same experience & aren't from the South learned to see watermelon differently - kind of like the scenario that
@Gumbo4x4 posted.
The racial history is there - like in the interesting article that
@sunshinehighway that posted.
But, in the south, our cultures & traditions have grown & mixed in together - we all eat watermelon & fried chicken, so to many of us watermelon is just watermelon, & we don't see the connotations. Over the years, watermelon went from being the racial stigma as described in sunshinehighway's article to a just general southern thing. I mean, we've all sat on the back porch & had watermelon seed spitting contests.
The South, as a whole, is heavily influenced by the African American culture - food, music, literature, etc., & I love how the traditions & cultures have blended together, which, to me, is part of what makes the South special.
And, as an aside, *is* watermelon just a southern thing? Do other regions not eat watermelon?