To repay even the smallest grievance is what 'taking revenge for a glare' means.
Tips
culture
Famous in the idiom 睚眦必报 - literally 'an angry stare must be avenged,' meaning someone so petty they pay back even the slightest slight. 睚眦 here means a hostile glare.
Eye radical on the left, 目, a pictograph of an eye turned upright. It fixes the meaning on a part of the eye. Same family as 眼 eye, 睛 eyeball, 眨 to blink.
