diarrhea
The stunningly painful feeling McDonalds spent years of research looking for a way to trigger. It'll get you as soon as you're finished eating and try getting up.
If you have a long road ahead of you after you get out of McDonalds, you'd better use the toilet before you leave, or you'll be painfully holding your diarrhea until you arrive home. Especially if there's blizzard outside, forcing you to slow down, and it's too late to stop anywhere.