Ooof, this has happened to me so many times, I know how much it stings and won’t go away. I know it sounds cliche and is hard to do; but try to let it go. Holding on to it is only going to hurt you and give that asshole customer more power over you than they already have. If it happens again (I hope it doesn’t), my favorite approach to asshole customers is taking the lay-on-the-guilt approach: when they start to go off, say “Sir/Madam, I have a stutter. It is a disability. Why do you think it’s ok to be mean to disabled people?” Then say nothing else and just stare at them. That type of silence makes people really uncomfortable - and the first person to break it basically loses that interaction and sense of power. Whatever they say next, just be really cold and make a LOT of eye contact. It will be more effective than arguing. And will give you back a sense of power than will take away some of that negativity. This might sound mean but think of how mean they’re being to you - and it isn’t like you’re saying something that isn’t true, or saying it in a disproportionately cruel way.