I find it so annoying when someone in (or who has been in) a relationship tells me to be happy about being single. They can't understand the point of why I'm upset if they've had the luck I haven't.
(wow my phone did some weird formatting to this post! Fixed now)
And more annoying that's its pretty much a stranger, a girl I went to school with over 10 years ago and was never friends with at school anyway. I need to be more selective with accepting Facebook friend requests.