I'm not exactly sure. I don't think Charlie Sheen does either.
Adonis was a figure in Greek mythology. He was beautiful, so beautiful that Aphrodite fell in love with him. She had Persephone take care of him and Persephone also fell in love with him. Zeus made him spend 1/3 of the year with each and then the last third with whoever- he chooses Aphrodite.
Adonis is a figure of beauty, youth and renewal. Perhaps Charlie means that he will be back even better?
Or Charlie is just crazy.