[cringes] A very sadistic older male primary school teacher once used this to humiliate me in front of the class
My Mum was an English teacher and always corrected our grammar, so I grew up using "may I" if I was requesting permission to do something.
Each class had a "communal" heavy-duty pencil sharpener on the teacher's desk, so I went up and said "may I sharpen my pencil?" - not loud, everyone else was working/chatting etc, but the teacher raised his voice (he was very scary so everyone shut up straight away) and said "Did you hear that children? LemonyAle said 'MAY I sharpen my pencil' not 'CAN I sharpen my pencil'. We all know she CAN, but it's up to me whether she MAY or not".
Cue mass daggers from most of the class - I was a bit of a swot but trying hard to fit in (aged 9 in the next year up), and this just set me back to square one trying to make friends