The very uncomfortable sympathetic feeling experienced while you watch someone else embarrassing themselves. This feeling is often intensified when the person embarrassing themself is not aware of how embarrassing their behavior is. In this case it is more like you are feeling the embarrassment on their behalf.
George: OMG, dude...this talent show is killing me. The fat girl dancing to 'Ice, Ice, Baby'...
Dude: I know man, I know...all the wrong things are jiggling--
George: --And her dancing! Everyone is laughing and she just keeps going. It's like a trainwreck right now. I don't even want to watch!
Dude: Total vicarious embarrassment right now, man.
George: Ugh. Let me know when it's over.
The personal embarrassment that one feels on account of and for another (i.e. a friend, a family member or a complete stranger) who is making a fool of him or herself. A person experiencing secondhand embarrassment feels as if they are doing the embarrassing action themselves, effectively putting themselves in the other person's shoes.
Guy 1: Man, Sarah's presentation today was terrible. She forgot half of it and stumbled through the rest.
Guy 2: Oh I know. I had so much secondhand embarrassment for her. It was like watching a train wreck.