DEAN: Don’t go.
JESS: Oh geez man, she’s not shipping off to ‘Nam.
Jess sardonically compares Dean’s distress over Rory going on a picnic with him to someone being sent to the Vietnam War (1955-1975).
Although the US had been involved since World War II in a very limited capacity, the first US ground troops arrived in Vietnam in 1965, reaching a peak in 1969, by which time more than half a million Americans were stationed in Vietnam. This was also the year in which the dreaded draft lottery began, where young men were called up for service based on their birthdate.
Opposition to the war played a key role in sparking the Civil Rights Movement and the hippie counterculture, as well as wide-ranging changes in popular culture. The last American troops pulled out of Vietnam in 1973, by which time there had been more than 58 000 US casualties.