몸 건강히 잘 지내, 친구야! 몸 조심해, 친구야! 잘 지내, 친구야! 1. When you are saying goodbye among friends or to the people casually, you can say like the ones above; drop -요 for the plain casual vs. the informal polite speech with -요. 2. Usually you don't need to add 'my friend 친구야'.