I'm going to purposely intimidate my girlfriend's ex.
Why are you going to do that?
He keeps threatening us online.
You should avoid possibly committing a crime intimidating someone. You can file a stalking report on her ex with the police.
It's funny because he is just a pathetic loser who has nothing else to do.
It is wrong to intimidate others and even though you don't like your girlfriend's ex, you shouldn't throw more fuel on the fire. He may just be upset that she has a new boyfriend so giving him more attention will make him do it more. He should be ignored and he will eventually give up.