On Twitter a Self Invitation is No Invitation

Dear Cyber Sorter,
I was on Twitter the other evening and bumped into a couple of good friends. We ended up arranging to have coffee. We didn’t go to direct message because there were four of us.
Then an acquaintance of mine tweeted all of us asking to join in.
She is a very nice person but completely out of context with my other friends.
I felt I couldn’t say no, but it will ruin our gossip because I know her in a professional capacity and my other friends in a private, personal one.
Was it reasonable of her to hijack our social group via Twitter?
CF

Dear CF,
Not really. It’s never a good idea to invite or insinuate oneself along to a social gathering without first being encouraged in some way. Look at The Talented Mr Ripley.
All Twitter friends were not made equal and less socially adept users often make these sorts of awkward blunders. The organic open nature of chat between friends on Twitter lends itself to this kind of conundrum.
This is one of the reasons making personal arrangements on Twitter is ill-advised. Unless your tweets are protected, it is more public than Facebook or LinkedIn.
The general rule is that after a couple of tweets, take your conversation off the stream and direct message your close friends, suggesting a move onto a private group message on Facebook or email.
This time, respond gracefully and see what comes of it. You never, know, she might be your next new bff . . . just don’t get in a boat with her.