Related to me by some friends tonight:

They were returning to LAX on an overbooked UA flight. The FA was asking for VDB volunteers, offering a free ticket and guaranteed seat on the next flight out as incentive. A man sitting in front of them decided to take the offer, got up and got his carry-on out of the overhead. He headed up the aisle as a young woman, evidently an inexperienced flier, was coming down to take the seat. She seated herself and asked her seat mate why the man left. Her seat mate explained that he accepted the offer of a free ticket and seat on the next flight out.

"Oh," said the young woman. "Where does the next flight go?"