Dear Mr X. -- You are a pretentious fuck and no one has told you because they secretly fear you are a sociopath.
Hello Mr. X -- You are a decent human being. Congratulations on mediocrity.
Hey! -- You are a bit dim and over energetic but are quite fun to be around.
Hi -- You give no fucks. Go home; it's fine.
(no salutation) -- You are an enigma (or just lazy/efficient)
Greetings! -- You are the kind of creep who watches too much anime and learns a language to try to seduce the women you fetishize.