You can't believe the words that have just come out of your mouth. You certainly didn't mean to insult the woman in line ahead of you, but it's too late now. What business is it of yours how many chicken nuggets she orders? She's staring at you angrily. You feel a sudden jolt as your heart rate increases. You have a coppery taste in your mouth, and your cheeks begin to feel warm. You, my friend, are embarrassed, and you're blushing because of it.
Howstuffworks "Why do people blush?"