I watched a documentary about them and promiscuous doesn't really cover it. They literally fuck each other as a hello. From another source:

Furthermore, sexual interactions among bonobos occur in every possible partner combination regardless of age or gender with the notable exception incest among siblings. These interactions reflect a much broader sexual lexicon in bonobos than in chimpanzee; in addition to vaginal, bonobos utilize oral and manual stimulation in a variety of copulation positions, preferring ventro-ventral position as in humans. Together, these differences in behavior suggests that sex in bonobo society serves a fundamentally different purpose than in chimpanzees that is not limited to reproduction. The differences in the behavior of these two species, however, is not limited to sex. Male chimpanzees express dominance over their female counterparts; by contrast, dominance is not strictly ordered by gender in bonobo society despite the fact that female bonobos are smaller than males (de Waal 1995).