people who invite you to an event on facebook, then invite you in real life, to which you reply yes (like a normal person) then get arsey when you turn up because they were not expecting you.
after all why would you be going if you didn't say so on facebook! f**k all this social network nuts
This!!!!! X1000
Sort of had that ay my bosses wedding last summer, I replied with the RSVP slip on the invite, TOLD him I'll see him at his reception the day before and when I turned up with the wife they were like

"Oh glad you made it!" srsly?

I fricken told you I'd be there! I even took the wrong postcode down from the invite and ended up at his in-laws house on the other side of the county, realised this, looked up the location and got there an hour late...
Only time I've ever had anything like that though and probably because whenever there is a function on I'm invited to I usually am already busy so have to decline.