Heat olive oil in a large skillet over medium-high heat. Season the pork butt with salt and pepper. Sear pork on all sides, about 2 to 3 minutes per side. Add pork to slow cooker. Add 1/4 cup water to the skillet and scrape off all the browned bits. Pour liquid into the slow cooker. Cook on low for 8 hours or high for 6 hours.
Meanwhile, make the coleslaw. Mix the mayo, vinegar, sugar, salt, pepper and poppy seeds. Stir in shredded cabbage and refrigerate until ready to eat.
For the cornbread: Preheat the oven to 350 degrees F. Grease an 8x8 pan and set aside. In a large bowl, whisk together the flour, sugar, cornmeal, baking powder and salt. Set aside. In another bowl, whisk together the milk, eggs, oil and butter. Fold wet ingredients into the dry ingredients until just combined. Pour into prepared pan. Bake for 35 minutes, or until golden and a toothpick comes out clean.
After pork is done, remove it from the slow cooker and shred it. Reserve 1/4 cup cooking liquid then dump the rest. Place pork back into the slow cooker and add the reserved liquid and desired amount of barbecue. Keep on warm setting until ready to eat.
Cut cornbread into four equal pieces then slice each in half width-wise to make 8 thin squares. Place a square of cornbread onto a plate. Top with desired amount of pulled pork then top with coleslaw. Garnish with pickles, if desired.