With a sharp knife, remove the corn kernels from the cob. If you've never done this before, just hold the cob vertically with the thick end on a cutting board and carefully slide the knife down the side of the cob, turning it and repeating until all of the corn has been removed. Alternatively, if you have a mandolin, you can slide the cob across the blade as you would a carrot, cutting lengthwise. Take care with your fingers and turn the cob in order to remove all of the kernels.
Scoop the corn up an place the corn in a bowl.
Peel a red onion and cut it in half. Cut each half into very thin slices using a knife or a mandolin. Add the onions to the corn and toss gently.
Add 2 1/2 cups of arugula to the corn and onions and toss gently.
In a small bowl or a mason jar as I prefer, combine the olive oil, lemon juice, salt, pepper and thyme. Pu the lid on the jar and shake OR mix the vinaigrette with a fork.
Pour the dressing over the salad and toss lightly. That's it! Enjoy. (Scale up to feed a crowd.)