There's always the people who you can sarcastically approach with this though.
You can type it like a nice guy but still get the message across, if there's a larger context of the two people disliking each other.
Who's to say if it's a genuine greeting or sarcastic poke at someone?
I can't see this ever being in the clear. The rule against it will be broken for sure, and at least in this day and age there will be people sensitive to that kind of word.