Apparently '80's pop star Tiffany was on Bravo's Watch What Happens Live and was asked about her relationship with New Kids on the Block member Jonathan Knight (Disclaimer: he was my favorite). She responded, then said something like, "And then he went gay." (Edited: I looked it up and what she said was "He became gay later." She was laughing while she said it, so I didn't understand perfectly.)
The problem? Jonathan has never come out publicly, though there has been speculation. Tiffany didn't realize this and later tweeted an apology, saying she hadn't realized that Jonathan hadn't come out.
Jonathan tweeted back very graciously that it was no problem and he found it funny. (Did I mention he was my favorite?)
I know there has been some disagreement on the board as to whether or not Twitter is an appropriate venue for apologies, but I thought this was handled pretty well. As opposed to some other recent unauthorized "outings," this one seems to have been a genuine misunderstanding and was handled well by both parties.