In a large bowl, whisk together the vinegar, sugar, salt, and pepper. Add the Vidalia onion and cucumber. Marinate for 1 to 2 hours at room temperature.
To the bowl, add the tomatoes, crabmeat, olive oil, green onions, and basil. Toss gently. Serve on a bed of lettuce or drain slightly and serve "naked".
Recipe courtesy of The Deen Family