Student or Learner
I always heard the little kindergaten always said "Hey' to each others. I pernsonally feel that it's not a decent and polite way to say. I always aske them to say "excuse . Am I right?
Those of us of a certain age remember hearing "Hay is for horses. Say 'excuse me.'"
Not just "excuse" but "excuse me."
It's hardly "indecent." It's just not as polite as other options.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.