Nǐ bié zhème xiǎoxīnyǎn, tā zhǐshì kāi gè wánxiào.
Don't be so petty, he was just joking.
Tips
memory
小 (small) + 心眼 (heart-eyes, i.e. mental capacity / outlook), someone with a 'small heart-eye' has a limited, petty perspective and takes offense easily.
