This will be a difficult task, and your chances, of success are low; but you could try something like:
"I need you to stop hitting me, as I don't think that our relationship can go on, or be healthy, if you don't. I show you enough respect to not hit you, and I deserve the same respect in return. If you can't deal with this or you don't think you can stop; then it's our relationship that needs to be over."
1st tell him to stop and then it dosnt matter if you like his girlfriend or not tell her
Ask her to stop. Tell her you're not interested in her.
Tell him that it is very impolite. Make him understand that she is your girlfriend and he should stop undressing her with his eyes.
Calmly remind him of the fact she is already with someone, and ask him to stop.
tell him/her you don't want to be their girlfriend/boyfriend! if they don't stop tell them to stop or else you will slap them!
Tell him to stop and tell her he's doing it.
You should tell your school principal or teacher if it is happening at school, or a parent if happening while not in school. or you could move school
sorry, misread. I would just tell him straight "sorry, but I am not interested".
Stick your D in her mouth /problem
Tell them to stop before either their skull or the wall is damaged.
if you or your girlfriend are constantly fighting then theres only 1 way to stop fighting and that's simply ending it or....... do something completely stupid and tell her you love her.
tell a little white lie, and say "there are cops coming!"