The uncanny hands-but-not-fingers movements they all do really bothers me. Their hands flop around but stay completely limp. Like they're robots who heard that humans move their hands when talking but don't have any fine motor control.
According to what I was told by some FANNG people (I've never worked for them myself) some employees were/are were sent to public speaking classes after being hired specifically to teach socially awkward programmers how to talk on stage, and this is what they teach them, weird hand movements and all.