It is not advisable to frequent deserted beach areas. You should never put yourself in a position where you can't be seen or heard by others should an emergency arise or you need assistance. Nude and topless bathing are frowned upon in Thailand, and showing a lack of modesty could unfortunately be misinterpreted by others as a statement of your own level of morality and intentions -- be aware of your dress. When you are in more remote or very quiet areas, you should consider your options for seeking assistance should an unlikely event like a robbery or assault occur or you become injured.