Consider: Yondu is lurking on some distant planet, waiting for news of a job, when he sees a woman he recognises. She’s sweet and innocent looking, downright motherly, but last time he saw her she was dragging him, and children like him, out of cages and selling them on to new masters. You don’t forget the face of someone who did that to you.
So he roughly calls Peter over and tells him to stand guard, and hands him the best gun they’ve got just in case any trouble starts. Then he goes after the woman and kills her. She knows her past has caught up with her, but she still pleads for her life.
“Please don’t kill me.” she begs. “I’ve got a child!”
Yondu sends his arrow straight through her heart. “So’ve I.”