Machete speech
Your girlfriend's dad (or your dad) gives the boyfriend a long talk that sounds like a death sentence. He might sharpen a knife, clean a gun, or just stare you down like you're the last person on Earth.
My dad stared me down like I had just killed his favorite dog and said, 'You hurt her, I'll kill you.'
My girlfriend's dad cleaned his gun and said, 'I'll shoot you if you don't treat her right.'
My dad sharpened a knife and said, 'You mess her up, I'll mess you up.'