psach libi bsorasecha; You should always say Hi!
Of course you shouldn’t shout “HELLO!” arms flailing,
jumping up & down.
It should be a quick Aidel greeting no stopping to schmooze.
Even if you don’t plan on continuing it.
Unless you notice that she/he noticed you and are trying to avoid you. Then don’t chase them to say your hello,
that’s not being polite.
My policy is L’olam Yehey Adom, Always be a mentch, don’t be afraid if ppl see you that’s not your problem & their job is to be Dan L’kaf Zchus, and not to turn it into the latest neighborhoods gossip.