People who can't let you finish a sentence without interrupting.

I have a certain relative (not my wife) who did that to me repeatedly last summer when we had some important family matters to discuss.

It's not like she doesn't pay attention at all. She pays careful attention to the first half of your sentence, and from that, she figures out what the second half was going to be, and then she can't wait to reply to what she thinks you were going to say.

Even when you point out she totally had the wrong end of the stick, she still doesn't take the hint and apologize.

It drives me nuts.