In Act 3, Scene 2, after Hermia accuses Demetrius of murdering Lysander, Demetrius responds with the lines in the passage:

"So should the murdered look, and so should I,
Pierced through the heart with your stern cruelty;"

Here, Demetrius is saying that he feels like a victim, "pierced through the heart" by Hermia’s "stern cruelty."

He compares himself to a murdered man, implying that Hermia’s harsh words and lack of love for him are cruel. He feels emotionally wounded by her rejection.