Many of us are raised to value other people's feelings above our own. We have to unlearn that, set healthy boundaries and not be so damn NICE and understanding all the time.
I agree with BerberElla - giving others another chance often just leads to being taken advantage of yet again. But start acting differently and others will start treating you differently.
I had a realization with a friend over the weekend - she gave a toga party, but when I showed up, I was the only one in a toga! I was mad and let her know it. But the biggest part was that I knew she would continue to let me down in various ways as long as I let her. There's no way I'd ever go to a party of hers in a costume again because I see she can't be trusted.
Somehow being embarrassed at her party brought this home better than years of waiting 45 minutes for her to show up and other acts of thoughtlessness. I already make very cautious plans with her and it's going to be a long time before I feel up to it again.
Embarrassment in public is harder for me than just about anything else. Unfortunately, it's usually me that does it to myself, but if I had a friend who embarrassed me and I thought it was done maliciously, she would never hear from me again. I also give people the benefit of the doubt but not over and over again, I drop them.
I was the INFJ kid who sat as far away from the teacher as possible. I had a best friend in high school who had a bit of an ugly streak (turns out she was slapped around by her dad alot). One time I was wearing a skirt that had a big zipper right up the front. I was passing out papers and when I came to my friend's desk she reached up and pulled the zipper down. I barely caught my skirt from falling off (thank God I had a slip on) and several of the kids, including her, were laughing their asses off. I was so embarrassed I wanted to cry which would have been even more embarrassing. I ran to the back and zipped my skirt back up and when I turned around my friend said "Oh my God, look how red her face is!", I walked over to my friend and pulled her out of her desk by the hair which made a lot of noise because the desk fell over too. At that point my intention was to drag her out into the hall where I could beat the crap out of her but the teacher grabbed me from behind and pulled me off. I was suspended for 3 days.
The tough thing is, I've never had more than one or two really good friends at a time so I'm more likely to put up with their untimliness, changes to plans, etc., but eventually I get sick of it then I quit responding.