To make classic dipping sauce, combine the fish sauce, lime juice, rice wine vinegar and sugar in a small bowl, mixing until the sugar has dissolved. Add the garlic and chilli.
To make lemon dipping sauce, combine all the ingredients in a small bowl.
Whisk egg whites in a bowl until light and fluffy. Put flour and coconut onto two separate plates. Heat a deep pan or wok and add oil.
While the oil is heating, toss one prawn in the flour, dip it into the egg whites and roll it in the coconut. Set it to one side. Repeat with the remaining prawns.
Once the oil is hot enough (drop a coconut shred into the oil and it should sizzle), carefully lower the prawns into the oil in batches of five. When the coconut has turned light brown on one side, turn the prawns over and cook until crisp and golden on both sides. Remove the prawns and drain them on paper towel. Serve with the two dipping sauces.