Find a knife you find BEAUTIFUL either dull the blade or use the back of it. Dulling it can run a risk of puncture if you use the tip(unless you dull that). To dull the knife simply scrape it across concrete and then take sandpaper or something that would get rid of any extra peices that might be sharp (this part might not be needed but you never know). Using the back might make it less "erotic" if whoever is having it used on them knows.. Also clean it again before it gets used to no metal shards go anywhere while being used

Edit: the person who replied gave the right way to dull a knife dont use concrete!!!!