Jane Fonda, like many people in the era, opposed the Vietnam War - during a time when the administrations of Johnson and then Nixon characterized opposition as "un-American." The slogan "Love it or leave it," was applied to anti-war protestors, indicating that if one were not in support of the war one was un-American and should leave the country as a traitor.

Fonda took this a step further by traveling to North Vietnam in 1972 and very publically voicing her opposition against the American war effort. A photograph of her sitting on an anti-aircraft gun, the sort used to shoot down American pilots, either killing them or causing them to be captured, was regarded as particularly offensive. She won the name "Hanoi Jane," which has largely silenced her, politically, for the rest of her life: every time she has had something to say in support of a liberal cause, the right simply says "Hanoi Jane" - meaning "traitor of the worse kind" - and anything she says is made to be irrelevant.

See this article, for example, to understand how Fonda herself views the incident.

On a personal note, [censored].

edited: a personal observation from the period has been deleted.