I was only 6 when he ran in '68, but I remember reading later that hippies supporting him went "Clean For Gene"
(from wikipedia):
"In 1968, McCarthy ran against incumbent President Lyndon Johnson in the New Hampshire Democratic primary, with the intention of influencing the federal government—then controlled by Democrats—to curtail its involvement in the Vietnam War. A number of antiwar college students and other activists from around the county traveled to New Hampshire to support McCarthy's campaign. Some antiwar students who had the long-haired appearance of hippies chose to cut their long hair and shave off their beards, in order to campaign for McCarthy door-to-door, a phenomenon that led to the informal slogan "Get clean for Gene."
"When McCarthy scored 42% to Johnson's 49% on March 12, 1968, it was clear that deep division existed among Democrats on the war issue. By this time, Johnson had become inextricably defined by Vietnam, and this demonstration of divided support within his party meant his reelection (only four years after winning the highest percentage of the popular vote in modern history) was unlikely. On March 31, 1968, Johnson announced he would not again seek the presidency."