My girlfriends ex wants to attack me?

Remember, your teacher doesn't teach you to get into fighting, you learn it to defend yourself. I'm too learning muay thai but I just wanna get ripped and so I can defend myself. Don't EVER start a fight unless they attack you first then you'll have the right to beat them up (self defense) but just until they back off, if they back off but you don't stop then u'll be the one who will get into trouble. Just don't listen to them, if you can't hold it you can bluff him directly in front of everyone if he's man enough to fight you 1-1 or he's a , make him angry so he knows that you're not afraid of him, he'll probably be scared and doesn't wanna pick on you anymore. By the way don't believe him when he said he's gonna knife you, he's just bluffing, he's just 16 years old anyway.