Hey, johnjohn--good to see you!

If Jackie was being a lot admonishing, she might have said "Buster". You got that right, Dudette!

I've used Bub all my life, 90-some-odd percent of the time as pure teasing. All I can suggest is try and go by context, which if it isn't clear here, please ask me--though usually I try to put unmistakable indicators when I'm being serious.