If you tend to hold a grudge, you don't let it go when you feel someone's insulted or wronged you. I hope you won't hold a grudge against me for bringing it up.
Grudge comes from the now dead Middle English word "grutch," which meant "to complain or grumble." Someone who bears a grudge might often be grouchy. You can specify a type of grudge: political grudge, personal grudge, etc. You know Grandpa's been holding a grudge against the neighbors for years, but you have to wonder: How long can he hold that shotgun?