line-jacking

Verb: When a person steals comments or lines that he/she overheard or read and uses them as if the comment and/or line was theirs. He/she might use bits and pieces of the comment/line, or the whole thing.

Jessica: (talking to Alyssa) The iPhone is a fantastic piece of technology that has transformed people's view of a quality phone.
Alyssa: I definitely agree.

Alyssa: (talking to Mark) Yes I love the iPhone. It is a fantastic piece of technology that has transformed people's view of a quality phone.
Mark: Dude, stop line-jacking. I heard Jessica say the exact same thing.