''You look fat in ...''

1) Why They Hate It: Woman are tring every kind of stuff for the people they love. You could say ''You look fat in this dress.'', but you don't think how sad she will feel since she might have been more than a hour picking this dress to impress you.

2) Reason They Hate It: Calling your girlfriend "fat" won't make you are hero, even if its true. You are supposed to like her in ever shape and clothing. 

3) How Will a Girl React If You Say It: ''Really? I though I looked okay with it.'' She might get angry even.

 4) What To Say: ''You look hot/amazing/sexy in...'' Trust me, you don't know how happy she will be when she hears you approve what she is wearing. You migh get even a kiss for a reward.