This should really be in ideas-wanted because it's such a great and much
needed addition.
Here goes: The high-five emote should ask the target "Do you want to
respond?", and if you answer no, the result would be an embarassing miss!
Best idea ever, implement right away!

For realism sake, there should be a check to see if your race REALLY DOES have
a hand at all, much less five fingers! This will make players become deeply
enthralled by even more realism. EX: 'You try to highfive Entor the Ent,
but only end up impaling your hand on one of his branches! Oh god, there is
blood everywhere!'

Best idea ever^2