My post for today just completely fell apart on me and I don't have time to work up another, so you're just going to have to content yourself with this image, deemed by myself, and esteemed Batmanologist (the esteeming is also self-generated) to be one of the greatest costumes ever worn in Gotham City. From Batman No. 234:
She only made a one-panel appearance and her only role in the story was to be threatened by a clown while riding around on a hot dog float, but Mustard-Hat Lady has found a place in my heart. I like to envision some fairly unlikely alternate universe in which she defeats the clowns on her own and joins the Batman Family in their never-ending vigilante crusade. I'll bet that Condiment King gets a bit more respect in that universe, too.