Some joggers weren’t joking when they said they were going out for a “brief run.” In briefs, boxers, bras and bloomers, they ran three-quarters of a mile in a Valentine’s Day-related charity event benefiting sick children. Saturday’s annual Cupid’s Undie Run featured 1,000 people in their underwear and little else, except for maybe some body-painted hearts, angels and Cupid’s arrows on their chests. Participants, some of whom shaved hearts into their chest hair, ran through the streets near the city’s sports stadiums.