When explaining why my job exists and what I do to non IT folks the easiest real-world example I commonly give is Black Friday. Everyone knows that Black Friday means millions descending on shopping malls. (In the good old days you had to show up at 5AM or earlier to get the best deals.)
Now many of those same deals can be obtained via online. As more and more shoppers look to Black Friday and Cyber Monday for the best deals, the pressure put on e-commerce solutions grow every year. Even though every year the large retailers know its coming, it never fails that multiple stores experience slowness or in some cases complete outages.
Below are a few links that detail some of the worst hit stores.