It's one of those lovely weirdo filters that life provides. It's a huge red flag that they are for some reason not socially compatible with me, mainly as I instantly feel like they're a total weirdo. I don't know exactly what's wrong with it, but it makes me feel like they are trying really hard to make sure I like them.
If it's when saying goodbye or hello that's completely different, but any other time is really bloody weird.
Note - this is only applicable for men. It is a total non-issue if a woman does it.