This happened during 1993-94 when I was in Standard 8 (Grade 8 or Class 8 as it may be called elsewhere) at St. Joseph’s High School, Bajpe – Mangalore, a school run by the Christian Brothers. One of the Brothers used to teach us English and Math. He had a little red book which he used to carry to the Math class, and used to call it the Magic Book. He would be at his strictest best when teaching Math and at his comic best when teaching English.
During one such English class, he taught us that “may” is the preferred word over “can” when seeking permission to do something. Because, by using “may” one asked for permission to do something, while by using “can” one asked for confirmation on ones ability to do that thing. This was best exemplified the next day.
The following day the students got some quality time between the departure of the teacher who took the class that had just finished and the arrival of the Brother who taught us English. The students wasted no time in creating a ruckus. When the Brother arrived, he saw what was happening inside. He peeped in and all went hush. He then asked with a smile, “Can I come inside now?” Out came a prompt reply from one of the students, “If you have legs you can come inside.”

(PS: The Brother took it sportingly and agreed that he should have asked, “May I come inside now?”).