Not sure it if has been mentioned already but the bizarre habit of sending emails from your smartphone when you require something 'urgently' rather than selecting that little keypad, punching in some numbers and speaking to the person.
A typical example is;
'I've got a meeting in 10mins/ I'm currently sat with someone: can you please send/ confirm 'something''.
This is usually CC'd into as many people as possible for which I now assume is the senders attempt at showing they were being pro-active and you are the person hindering them for having the gall not to be glued to your work email.
These people also tend to send emails about 1min after refusing to answer your attempted telephone call.