'You Are So Fat!'

March 25, 2008— -- For visitors and residents of Long Branch, N.J., it was a typical, tranquil day at the beach — until they heard three young, bikini-clad women spouting insults at a woman on the boardwalk.

"Oh my God! You are so fat," one of the girls said. "How could you sit here and eat like that? Have you ever tried lipo? What about gastric bypass?"

The target of the girls' vicious remarks was a middle-aged woman sitting on a bench and snacking on a few fries while trying to enjoy her book.

"Please just leave me alone," the woman pleaded.

The language was no doubt disturbing, but the three young women and their victim, Cynthia, were actors taking part in an ABC News experiment. We lined the boardwalk of this Jersey Shore town with hidden cameras and kept a watchful eye on the scene from our control van parked nearby.

The purpose? To find out what people would do if they saw three teens verbally harassing a woman simply because of her weight.

Most passersby appeared oblivious. Fourteen beachgoers walked by without even glancing at the actors, despite their clearly hateful remarks.

Then, a woman named Elayne walked by with her son, Alex, and the girls no longer went unnoticed. Obviously concerned, Elayne and Alex looked back several times as they walked past but chose not to stop.

"It's very unfortunate, you know, how they could be so mean to each other, but I wasn't going to get involved," Elayne said. "Sometimes you have to just be like 'D-G-I, don't get involved.'"

"[Alex and Elayne] could have seen it as really not that bad, not deserving of an intervention at all, or they could have seen it as something that wasn't their business," said Carrie Keating, a social psychology professor at Colgate University.

Keating was shocked at how few people noticed but chose not to intervene. She said this stems from a stereotype that overweight people only have themselves to blame.