As an adult I'm asking nobody if I "may" use the bathroom. I might ask, "can I use YOUR bathroom" (notably not "may") or say "can you point me to the bathroom" because I am a human being with a right to access these facilities (Americans need not apply).

Teachers who feel the need to get one over on a child are pieces of shit. It teaches nobody anything except "adults are awful". Be nice to kids, you can fuck them up with something you don't think twice about.