Hmm.....grudge...."a feeling of resentment harbored because of some real or fancied wrong"........"a strong feeling of anger and dislike for a person who you feel has treated you badly, especially one that lasts for a long time."
I don't think I have much in the way of long term grudges. Maybe a little bit towards one or two of my schoolteachers back in the 1960s, but strangely not towards my mother who must have given me as much pain. I suppose it's because I can see that my mother was a rather disturbed person, and therefore somehow beneath the required level of responsibility for judgement, while those cruel teachers seem to have had a lot more of a choice about their behaviour towards me - in those days teachers had a lot more freedom to do as they liked, and they certainly didn't seem terribly overworked or unhappy.
I have trouble resisting the temptation to discuss and lampoon some of the naff behaviour of one of my ex-wives when I recall it, but I don't think that's really resentment. It's more light-hearted than that, though as we were married a long time I do feel a bit of resentment that the relationship wasted such a large chunk of my life. Still, I understand that nobody forced me to stay with her, and when she'd crossed one line too many I got rid of her and thus "had the last laugh," if I may put it so crudely. I've had other partners who gave me more pain but these days I feel more sorry for them than I do for myself. I probably tend to emphasise their unreasonable behaviour when I talk about them, at least to a degree, but I think a lot of that is down to my desire to justify my own actions rather than to demonise them particularly.
I do tend to rather strongly resent people who are currently messing up my life or the lives of others who I care about. My neighbour who lives in the apartment above mine makes a hell of a racket, often right through until the small hours of the morning when I'm trying to sleep. I've named him "Tinkerbell" which is deliberately ironic because he's a clumsy "big-footed elephant." I would also like to take revenge against him, at least I think I would, though if I got the chance to seriously mess up his life then I'd probably not actually do that. But it's different because he's a current problem and I'll very likely stop denigrating him to myself and others as soon as he stops causing me pain.
I guess I entertain quite a lot of ignoble thoughts, and they can sometimes take the form of grudges. I don't feel particularly guilty about it because my behaviour towards the targets of my resentment isn't anything like so nasty as what goes on in my mind. I think it may be dangerous to try to sanitise my inner feelings too much. So I allow myself to denigrate in my own head as a kind of safety valve. I know I don't really mean it.