This USPS guy's telling me all this shit I already know, as if I'm an idiot

I've only been a damn mail clerk for ten years and have been working with USPS that whole time. I know how processing mail with them works! When he kept trying to explain shit to me, I finally gave an exasperated "I know, dude." He's all "Just want to make sure." It was starting to get offensive. I don't know if he thinks I'm younger than I look or just talking to me like because I'm a woman (not something I say lightly), but I was ready to get a bit unprofessional, it was annoying me so much.