I want to pick up a girl that my friend started dating.
That's bad. What are you thinking of doing in order to pick her up?
I'm going to break her up with my friend
I get being attracted to someone, but it sounds like she's spoken for. You need to leave your friend's girlfriend alone, and find someone else to date. You'll ruin your friendship if you don't.
I'm going to manipulate her into believing that my friend is a bad guy by talking to her.
That is an awful plan. Not only are you betraying a friend by trying to take his girl but you are also trying to manipulate this girl. You need to take a step back and think about what you are doing.