Here's a good one & it actually happened to me this week on FB
If you send a private e-mail to 6 people & invite them to a function guess what will happen if people start chatting back & forth ? EVERYONE of those 6 people can read the comments. Ok so far. BUT if you decide to gossip about one of those 6 people, guess what ?THAT PERSON CAN READ WHAT YOU ARE SAYING ABOUT THEM !
Yes I was the one they gossiped about b/c I declined a high school "chicks night out" & the one that did the inviting was talking to the others as to why I refuse to go out with them etc etc & that based on my pictures it looked like I only went out with my DH & DS. These were not people I was good friends with in highschool & only have re-connected through FB.
When I wrote back on the thread that I did in fact go out but just not with people I haven't seen in 20 years & specially people that still acted like we were in highschool.

It was priceless when the 2 gossiping harpies read that. They were falling over themselves apologizing & that'e not what we meant etc.
Needless to say we are no longer FB buddies