Use PLZZZZZZ a lot. :D Seriously though, as long as you don't target anyone and use inappropriate words (i.e. insults and "them's-fighting-words sequels") you'll be fine. Also, as people reflect to informality in different ways, (which means, one finds
hey there inappropriate while the other one looks at formality as sarcasm) this question renders "primarily opinion-based". All in all, I'll stick to
hello. —
MARamezani 9 secs ago