Needless to say means "obviously, unnecessary to mention".
Barb: Hey, Rob! How are things with you and Sandy?
Rob: Oh, you haven't heard yet? We broke up....
Barb: What? What do you mean? What happened?
Rob: Well, I went to New York for work last month.
Barb: Yes, I remember that much. You were there for 2 weeks, right?
Rob: Well, I was supposed to be there for 2 weeks, but they needed me back in LA after a week, so I came back a week earlier.
Barb: OK... Then what?
Rob: Well, I got home and Sandy was... She was...
Barb: She was, what???
Rob: Well, she was eating all my expensive chocolate. She knew that no one touches my chocolate!
Barb: That's so lame, Rob! Come on!
Rob: Well, she knew it, Barb! No one eats my chocolate! I got really upset and started to yell at her. Needless to say, she left and said she would never want to see me again...
Barb: I don't blame her, Rob... You are so weird!
This idiom was taken from our LSI book, Reading Horizons! For more information, please visit: www.languagesystems.com