As it happens, I do own a "round, microwaveable glass casserole." My mother made sure I bought one when I was moving out on my own, because she said it was essential to cooking many types of dishes. However, I absolutely never use it. Day after day I rebelliously misprepare my Pasta-Roni in everything from cereal bowls to plastic Tupperware dishes.
All my bowls are still round-shaped though. I think I should go shopping for square and triangular ones just for the sake of being more rebellious.