Customers fucking suck. These kinds of customers are entitled assholes who aren't where they wanted to be in life so they take it out on people they see as lesser than them, usually retail workers because they measure people's worth by how much money they make. I'm sure you did fine don't let it get to you. Just know that you're better than they'll ever be

First off, F*CK THEM!!! Second, it does feel disorienting and personal in the moment but if you can pay it no mind, do. What I realize the longer I stay at Starbucks is that some customers come in looking to fight/demean/berate and you could be the world class record breaking barista champion and the most accommodating person, they’d still find things to complain about. They’d not walk away without a fight or making people feel terrible about themselves. What you do with these people is being ‘clinical’ about the ‘problems’ - what is it you’re not liking? too much coffee? Too much milk? Not sweet enough? This should throw them off enough. If this doesn’t work after the 3rd try, then just say ‘I don’t know what more I can do.’