Near the edge of park overlooking the freeway by the cliff off Quince is a popular area for sunbathing. Just lay back, watch the guys and see if there is any interest. Mostly in shape guys aged 20-40, dress in a bathing suit or briefs that looks like underwear to fit in.
From 163 downtown going north, take the Quince St exit. Go up the hill to and turn first left on to Balboa Park Street. The park is on the east side.