Put the bacon in a small skillet and cook over medium heat until rendered and just crisp and not black, about 8 minutes. Transfer to a paper towel to drain. Reserve some of the bacon fat.
Brush the corn lightly with the bacon fat and put on a baking sheet. Roast the corn, turning once or twice, until the some of the kernels get a little burnished, 15 to 20 minutes. Cool. (Alternatively, the corn can be cooked on a hot grill for about 10 minutes).
Dice and chunk up the tomatoes - it's kind of great if they aren't all uniform. Put the pieces into a big salad bowl and season with salt and pepper. Don't be shy - tomatoes come alive with salt and pepper. Strip the leaves off the thyme sprigs right into the tomatoes. Toss together lightly and set aside to get juicy.
Whisk the vinegar, mustard, 1/4 teaspoon salt and some pepper in bowl. Gradually whisk in the olive oil to make a smooth dressing.
Slice the kernels off the cobs add to the salad with the bacon. Add the arugula, season with salt and pepper and toss lightly to combine. Serve.