In no particular order of importance (and likely no overall importance whatsoever)
"Person you don't know wants to be your friend on Facebook"
"Who?" followed shortly by "Why?" followed shortly by "I really dislike Facebook already, I can't see how this will make it better." (Aside - Facebook is one of the few services that gets worse the more you use it. )
"Person you don't know has just followed you on Twitter"
"Person you know has sent you a Direct Message on Twitter"
"Please send me an email. I don't need another 'Inbox' to have to ignore."
"Person ABC has mentioned you in their 'Follow Friday' tweet"
"I remember 2008 too."
"Person you don't know would like to add you to their professional network on LinkedIn"
"Yes" followed shortly by "Please don't send me any LinkedIn messages. I don't need another 'Inbox' I have to ignore."
"Person ABC is now following you on Quora."
"Oh yeah, Quora. I should really try and attempt to answer a question on there someday.... Nah."
"Person ABC has added you to their Google+ Circles."
"People are still doing that? Huh."
"Steve - here are some Pinterest boards we think you will like!"
"Pinterest - it is pretty clear you don't know a thing about me."
"Person ABC started following you on Instagram."
"Be prepared to be consistently bored."
"Person ABC wants to be your friend on Foursquare."
"There are about three people that need to know where I am at any given time. You are not one of them." also "You will come to learn that I go to bagel shops a lot."
"Person ABC favorited you page on About.me"
"Now come on. About.me? Really? I am embarrassed to even have an About.me page."
It does all seem a little silly sometimes, doesn't it?