speak for (one)self
1. An imperative to express one's opinion as one's own, and not represent it as being indicative of anyone else's. The phrase is said when there is disagreement. A: "We just love traveling." B: "Speak for yourself—I think it's exhausting."
2. To express oneself, as opposed to letting others speak for oneself or remaining silent. She needs to speak for herself—I'm not a mind-reader!