Rinse the pork shoulder off and dry it with paper towel. Season the shoulder well, on all sides, with salt and pepper. Give it a little pat to make sure the s&p are really stuck on there.
Whisk the spices (cayenne - garlic) with the olive oil to create a rub. Use your hands to smear the rub all over the pork. Really rub it in there using the back of your hand or your knuckles. Place the pork in a cast iron pot or oven safe pot with a lid. Cover the pork ¾ of the way with water. Add the jalapenos and onions to the water, cover, and put in the oven.
Cook the pork for 4 hours, flipping it every hour. For the first two hours or so you won't really think that much is happening, but by 3+ hours it will start to be very tender. Be careful flipping it towards the end so you don't end up splashing yourself! When the pork is tender, remove it from the oven and the pot, and let it rest for 15 minutes.
Use two forks to shred the pork, or if you want it a little more roughly chopped use a knife. Pour the juices back over top after you've put it into a serving dish.
Serve as desired, but absolutely with limes.
Recipe by Cooking in Red Socks at http://www.cookinginredsocks.com/2014/03/17/spicy-pulled-pork/