Mistakes happen at milongas. It is funny how easily one can mistake an invitation for someone else as directed towards you. Cabaceo helps with this from what I am told, but it is not fail proof.
I found myself on the wrong end of an invitation a little while ago, and it would not have bothered me except that it was not handled well, and so I felt slighted a little and more upset at the correction of the invitation than the fact that the invitation was for my friend and not for me.
I was standing next to a friend of mine, who was sitting, and I heard a voice next to me say "Would you like to dance?" I turned around and saw the leader glance at me, so I thought that the invitation was for me. I said yes and then his face took on an embarrassed look and he said "Oh no, not you.... I'm sorry." at which point I realized that my friend was standing and that the invitation was actually for her, and my turning around must have caused him to look at me. Plus his approaching her "through" me, where I was between him and her, also contributed to the mistaken invitation. I quickly laughed, moved aside and sat down. But those words.... "not you" caused a little flame in my cheeks. If he had still been looking at his intended when I turned around, I would never have mistaken the invitation. Even if he glanced at me, but then turned his gaze back to his invitee, again, no mistake would have been made. But when the mistake was made, a slightly more elegant disentanglement would have been appreciated. Because even though he might have been flustered, to say to someone "Not you" implies a whole world of dismissal.
I have not been dancing long enough to know all of the proper codigos, nor have I been to BsAs yet to really experience cabaceo invitations. However I do believe that there are better ways to handle mistaken invitations without causing too much embarrassment for anyone involved.
One thing I was thinking of was that if this does happen, it would be very nice at some point in the evening to ask the person to dance. It does not have to be a whole tanda if the DJ is playing 4 or 5 song tandas, just for the last couple of songs of a tanda. It would be a very nice way to apologize for the error. I am sure many people will disagree with me on this one, but I think it would ease the situation and take away most hurt or upset feelings. I have heard that in BsAs if a woman accepts a cabaceo that is not intended for her, the gentleman will usually dance with her to avoid causing her embarrassment. This I do not expect and it does not really apply to North America as very few people truly use cabaceo here. Would I have accepted an apology dance from this leader? Most likely. Will I accept a dance from this leader in the future after what really happened? Questionable.
There is really no easy way around this sort of thing, but to allow the other person to more easily shrug off the situation would be appreciated I am sure.
Of course, all of this is from my perspective, a follower who is still gaining experience and learning. I would be interested to hear from leaders as to what their experiences have been and how they handle the situation. As well as anyone, leader or follower, who has experienced cabaceo mistakes and how they were best handled.