To become angry, agitated, or irritated. John always gets miffed over the traffic on his way to work. Don't get miffed with me, I was trying to be helpful! I got so miffed when I found out I was being audited that I threw my plate across the room.

Irritated and mildly angry. Typically used with modifiers such as "pretty" or "a little." I was a little miffed to find out the promotion had gone to someone else, especially after all the extra work I'd done for the company over the last month. You might want to give Mom a wide berth, Tom—she's pretty miffed at the moment.