Ms. Flamiel
From Loonipedia
Miss Flamiel made her first appearance in the cartoon Chalkboard Bungle. She is a very strict teacher that doesn't tolerate anything and writes an "F" on people's foreheads with a red magic marker (black in Wakko's case) whenever someone doesn't follow the school rules or do something incorrect. In her first appearance, she is hired by Mr. Plotz to discipline and educate Yakko Warner, Wakko Warner and Dot Warner. However, the Warners were able to deal with her. In the end, the Warners, disguised as Miss Flamiel, had her sealed in a crate and got Ralph, who thought the Warners were inside the crate, to lock her inside the water tower. Deispite all that, Miss Flamiel continued to be the Warners' teacher as shown in other cartoons, only this time she seems to be less strict and the Warners being more cooperative.