I think a lot of this type of thing boils down to boundary issues and commanding and/or demanding respect from others.
I'm lucky I have my husband around to observe mentally healthy behavior in. In my observations, I see him having responses to situations with other people, that are automatic trigger reactions which will put up an immediate wall not allowing the other person to advance any furthur with an inappropriate remark, comment or action. I'm still trying to figure out where this ability in him comes from, as I'd like to administer it myself during occasions calling for the need of it. The funny thing is,he really has no idea that this is a technique or ability, that he can do this. It's something that I feel is as ingrained in him, as much so as the reactions that I have to indignities are ingrained in me, that are directly the opposite of his (most of the time). I use his behavior and reactions as a template I employ when I'm uncertain of what reaction would best serve me.
And that is the bottom line: what serves you best? If a person is toxic, and repeteadly so, then is it in your best interest to have this person continuously undermine your efforts for a happy existence? The best course, I suppose is to determine when to pick your battles. The small stuff may not be worth your precious energy, and no amount of protestation will be anything other than adding kindling to a burning fire, a fire that may burn you in the outcome.
Humans will be humans, as much so, they will be animals too, in that a pecking order will be observed. Have you ever had a few pets at home, and one becomes old and ill, or just sick? I've noticed that the sick one will get F***** with, and the others will often pick on the weaknes, in an attempt to alter the pecking order to compete for the top position. Humans will do the same thing. People can manipulate, push buttons, bait and tease their way into being the superior one in a given situation. Maybe it's because they have baggage issues of their own, feelings of inadequacy and low self esteem, or ulterior motives. Sometimes it's a mystery as to why people will do what they do. But it's not our job to figure that out. Our job is to maintain our self and our own happiness, regaurdless of how others will react to that.
In answer to the original question: yes, I often do find it difficult to forgive other's treading upon my boundaries. But I also have the knowledge that it's more important at times for me to expend my energy in positve way, rather then to call them on some stupid remark. I allow them that remark, but I do keep a talley of how many of these remarks I will tolerate. The number will be random, and is directy connected with my own personal comfort zone, and how important the person is to me.
Emotions are not right or wrong, they just ARE. They exist and can be coped with to varying degrees. I do believe that an exploration of what your boundaries are, and what you're willing to tolerate, is helpful and will give you the tools to recognise in future interactions how to best deal with insensitive comments. I myself practice human interaction transgressions upon situations like the ubiquitous rude clerks or customer service relations people I encounter in the retail world. I worked many years in retail, and I know professionalism when I see it, so I therefore know when my boundaries are being tread upon in that type of scenario. I only wish i knew it better when dealing with others on a more personal basis

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I try to work on recognising that I never have to explain something I do in my life to any person, if it's not something directly involving them or hurting them in any way. If you want to buy a car with cash, that's your own business, and not the right of another to act as personal financial adviser to you. I should think a blantant stare with puzzling disdain and an internal shrug of indifference coupled with a barrier of silence, would suffice as an appropriate reaction (I'm envisioning how my husband might react). Not worth the trouble of even ackowledging a fruitless and insensitive comment such as this...JMHO.
Good luck with your teeth, that must be very painful to deal with and hope you can get those fixed soon. I do empathise with you.
Sun, sun, sun - high's in the 80's all week.