Genie Bouchard Ditches Mermaid Tail For Tiny Black Bikini On Necker Island

[[tmz:video id="0_zaxy8wf9"]] Here's Genie Bouchard proving two legs are a helluva lot better than one tail ... 'cause she ditched her mermaid outfit for a tiny black bikini Wednesday -- and we're all grateful for it. The tennis superstar has been over…