Lol do not follow any of the other replies here. At least play along a bit and see where it leads and to have how serious she is. I would probably laugh, sit up straight and say something like "rude!". And then look at her for just a second to see what she says. But not longer or it will be awkward. Then defuse it, still smiling and say some bullshit joke to defuse the short tension.

Dude if you're on a date, she is gaging you just as much as you are having her for a suitable match. You have to play along. You have to push each other's buttons and be a bit honest and also to see if the other person loses their shit over something small. It's called flirting and teasing. Play it cool and win another date. Be the bigger person. If you can play it cool and she's teasing too hard or even belittling you, then just walk off. Trying to lecture her or cuss her out is beneath you. But if you're on a date and it's going well and she says something like that, chances are she's just being playful. Lightly tease her back or throw in some self deprecating humor. But Jesus Christ don't get salty over something like that.