cut the bacon into small pieces and cook over medium heat until crisp: drain on paper towels and set aside until later
In a mixing bowl, combine the mayo, vinegar, onion, sugar, and raisins. Add the broccoli flrets and toss to mix well.
Add raisins and mix again. Refrigerate for at least one hour. Add bacon before serving. The bacon will get soggy and dressing will separate after being in refrigerator but could be done ahead of time.