Tell her ahead of time. Its really no big deal. Besides, as mentioned before, chicks dig scars. You may need to spice up your story a bit though... something that starts just a little over the top, then gets more and more crazy as you continue to the point where its impossible that you are telling the truth. You will have her intrigued at the beginning and then it ends up as a joke and you both get a laugh out of it and the stitches themselves are trivialized. Brilliant.😀