That salesperson could have had a fight with their partner that morning, or they're wearing poorly fitting shoes, or they just hate their job. The editor's flat out and has received over 100 emails that morning and the phone won't stop ringing. The friend's child has wet the bed again, another child has a fever and their husband's job isn't as secure as they'd hoped. Or they're just grumpy.
A more positive, optimistic frame of mind would help us all move through life easier. Obviously if you don't remember doing something to offend your friend, you haven't (or you need to revise your drinking habits). Thinking to yourself "This ALWAYS happens to me!" is the shortest route to assuring that crappy things will continue to be attracted to you. If you shrug, brush them off and move on, chances are things will be better tomorrow.
Change can often be a shock, but chances are it'll open your eyes to a whole new life.