No, it is just the opposite. In your example, the tailor is saying that you have a good body. The phrase "...would kill for..." means that something is very valuable, so valuable that someone would kill another person for it. It is NOT to be taken literally. Another example of its use is: "Look at that fancy car. I would kill to have a car like that!" A similar phrase is "...to die for..." It is often used when talking about food, such as "This chocolate cake is to die for." It means the cake is so good, you would trade your life for it. These are just overly dramatic statements used to make a point about how good something is. They are used quite frequently in US English.