In Cambodia, if you're considerate of local customs and norms involving modesty, you swim fully clothed: jeans, t-shirt, or maybe, if you want to show some skin, shorts. One of my girlfriends, a rather progressive Khmer woman, was admonished for swimming in a pool while she was visibly pregnant because it common knowledge that: (1) you don't swim when you're pregnant; and (2) you don't swim donning a bikini of all things.
You also do not engage in public displays of affection with a member of the opposite sex (e.g., couples do not hold hands while strolling outside), but it's fine for two young men to hold hands or caress each other as they ride a motorbike.
Gender relations and issues in Cambodia are a topic I have not documented here before. Let's just say it has been interesting.