1. To express one's opinion as one's own, and not represent it as being indicative of anyone else's. Used as an imperative when there is disagreement. A: "We just love traveling." B: "Speak for yourself—I think it's exhausting."

2. To express one's own opinion or point of view, especially in contrast to those of others. She needs to speak for herself—I'm not a mind-reader! Speaking for myself, I haven't noticed any of the problems that David is bringing up.