|Just be quiet. it always works.|
Better to ignore it and chalk it up to experience. If someone is rude to you, they are not worth your time or trouble. Don't dignify their rudeness with any reaction, which is what rudeness is all about anyway - provoking a reaction.
Remain silent and smile. Upon reflection later, you will regret any direct response that you offer - either it wasn't loud enough, or too loud, or it was too cutting, or not cutting enough. You'll inevitably come up with a better comeback hours later. Anything you do at the time, you lose.
Just smile. Even with them a nice day if you are in the mood. Then, move on to people that matter, because the rude one no longer does.