I think it would depend what they did. 

I have one old male friend from my late teens who ‘stood’me up for a couple of dates - not a problem with that! I never got particularly upset at the time. 

There were some female friends who just ‘dumped’ me in my early twenties when I had children because I couldn’t socialise anymore. I have tended to ignore the ones who haven’t send a message with it along the lines of ‘wow look at us all grown up with kids, how time had flown’ or something like that. 

It would all depend on what happened. 

A few years ago the worst of the "mean girls" from my high school friend-requested me on FB. At first I was shocked, she was so nasty to me for so long. Curiosity got the best of me, I looked around at her FB life- while she is still rich and beautiful, she has a young child with CP.  She often talks about how hard it is for her to have friends and how hurt the child is when other kids don't understand her leg braces. I think (based on social media) that she has grown as a person due to being a parent of a special needs child and I no longer feel any animosity towards her. 

Now if my abusive ex came knocking- I would do everything in my power to make him disappear again. 

I agree, it would all depend on the specifics of the situation but I have learnt in my many years that often when things are broken, it's because they are not repairable. This is why I stay away from ghosts from the past and their willingness to rekindle. There's usually a reason why I don't have them in my life. 

My skids bm has done plenty over the past 15 years to justify my pure hatred for her. If she sent me a friend request, I would laugh, show my dh, laugh some more and go on with my day. 

Yeah, it depends. But even if I didn't want to be someone's friend, I wouldn't walk off if they joined a group at a reunion, over a 40-year-old grudge (unless they had killed my pet or something horrific).

That's just attention-seeking.

If it was a person I had fallen out with in the past, then I would probably be able to hazard a guess as to whether they'd had the capacity to change or not.  Generally, most people don't change.  And if something about them would make me angry years ago, chances are it would still be in their repertoire of behaviour now.   I had a best friend for years, when I was a child, and when we were both 17 she stole my first boyfriend.  To me that displays selfishness of the kind I could never forgive or expose myself to again.  On the other hand, if it were a minor falling out or a misunderstanding, I might give them another go.  

There was a girl who was in my circle of friends when I was in HS... we were not besties.. but our school was small.. and our group of friends was probably fewer than 15 girls that hung out.  We even ended up being roomates my first year in college.. and THAT is where we had some pretty big falling out.  we were not compatible to live together.. and I would hazzard we both disliked each other a lot when we last saw each other in 1984..lol.  

But.. she is on my FB list of friends.. and we have connected loosely there.. we have commented on each other's posts etc..

Honestly.. I was a bit of a terror then.. and she was uptight and snobby.. we have both grown up.we don't live near each other.. we were army brats settling in diff areas of the country.. I think if we did attend a reunion.. we would be ok.. we were just girls who didn't mesh as roomates really.

On the other hand.. a sister of an abusive EX tried to keep in contact with me.. I finally had to tell her nicely that while she was a lovely person that I wanted to sever all ties from a very dark and unpleasant period in my life.  

When someone shows you who they are, believe them!

I am actually friends with a woman that cheated with my EX.  30 years ago.  lol

Of course back then, my world was turned upside down and I HATED her for many years.  I never talked to her after that and still have not.  She requested me as a friend about 5 years ago.  I was alittle shocked to see her do that but still accepted her request.  I mean it was so long ago.  

I wished so many bad things on her back then.  (late teens).  I am actually happy to say, it looks like she has a real nice life.  and has been married to the same man for many years.  She was not the viper I expected her to turn out to be,  She was just someone that made a mistake back in the day.  All water under the bridge.  

No clue.  lol.  Would not doubt it. 

People change some times..

If we were two real different people who just clashed I might give it a try. 

Some one who did something shitty to me I'll pass. Be polite unless its in-your-face like Grabitandgo. Then I'm done being polite and make sure they know to step off.

I think it depends on the maturity level of the person. I was bullied in junior high and high school, heck I have even had to work with a girl who told me she would kill me in junior high school. She doesn't remember me, but I remember her. I figure she was probably a very messed up kid, but it's good to see she got her life together and is doing well now, why remind her of some stupid stuff she did when we were all hormonal little a$$holes.

I had a friend request from BM a few years ago.  I personally think she did it to either 1. Be a smart add or 2. Accidentally while trying to stalk my Facebook.  I have it on lockdown so she can't see anything.  I had her blocked for years but unblocked her when YSS got a Facebook page.   Deleted her request. Then several months ago I got a friend request from BMs 80 year old dad.   I am sure it was really BM or her SO but I wasn't trying to find out.  Delete!

I will admit I hold grudges.  Not to the point I wish harm on someone who's wronged me for life.  But if I have cut you out of my life....there is no returning. I can be civil if forced to interact but there will be no deeper connection other than pleasantries.   I got a friend request from a woman I have known all my life.  Her daughter had an affair with my XH while I was pregnant.  She knew about it because they hung out at her house.   It didn't last long and I later found out the XH lies and said we were separated.  Don't care....don't need or want contact with her.   I think she feels bad about what happened with her daughter and my XH.  But I don't Need or want to rehash it.  I hope she has a happy life...just without me in it.

life is too short to give moments of it to people who don't value you.   
And in turn, I am sure there are people I have hurt in my life.  I don't expect them to forgive me and I won't push myself in them.   I figure the best thing I can do for anyone I hurt is to leave them alone.