The beaches in Phuket, especially in the south, are great for swimming, though, you should be warned that the rip tides take lives regularly, every year; Thais and westerns. You can still go swimming. But, if you find, upon entering the water, that the sand drops off rapidly, then you're in a possibly hazardous area for swimming.

As far as the sex goes in Phuket (Patong Beach), you'll get all that you want while you're there. And the place isn't nearly as busy as Pattaya.

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My Mouth Is Your Cum Receptacle...