Step 1: Purchase 1 or 2 pies (2 pies if your going for the value menu) and a plain McFlurry (no condements like smarties).
Step 2: Depending on how you would like to enjoy your Mac Pie A La Mode, you can take a chunk of pie and scoop some ice cream or (as I like to do it) make a hole in the center of the McFlurry and insert the pie, and taking scoops of ice cream and pie at the same time.
*There are other variations of the Mac Pie A La Mode such as mixing the pie in with the ice cream.
Person 2: "You should get a Mac Pie A La Mode"
Person 1: "What the hell is that?"
Person 2: "It's the best damn dessert in the world!"