It's not really offensive. It just means the person has the character of a "mad dog". It's probably a nickname. By the way, "i wanna know what does that mean?" should be "I'm wondering what it means," or "I want to know what it means." No-one will take you seriously if you write childish slang like "i wanna". Also, pay attention to question forms.

much thanks , but i dont want a translate to the word , when i search on google i found its an amercian expression which means some1 who acts in offensive (or another word i dont remember) manners اقصد باسلوب عدوانى ... i just wanna get sure of this ..thanks again

كلب مسعور