In the movie "Kristi and the Time Machine" at one point the main character has to fight a gladiator. At first she's losing, but then she arouses her opponent and then cuts his dick off! The effects are cheap (as is the whole movie), but I like the idea.
You can watch the whole here: http://ikinokz.net/6623-kristi-i-mashina-vremeni.html The fighting/cutting scene starts at about 73 minutes.