In the scenario which you've outlined, where you say "hello" to me, having never spoken to me before? No, I don't think that's an offence, but more to the point

In the scenario which you've outlined, where you say "hello" to me, having never spoken to me before? No, I don't think that's an offence, but more to the point, whether I did or not, the police are unlikely to. We don't operate in a system where the police simply take the word of anyone who reports a feeling, the police have a duty to assess whether a crime has likely occurred.