I'd forgotten the "May I". At school we had to use "May I" but at home things were more relaxed.
I quickly noticed the use of "excuse me" and also the use of "Sir" in America. Here we use "excuse me" for many reasons so that the tone -- as mayomick says -- is everything. It may be a sarcastic comment about being ignored.

Then there's the round-about (?Irish) way of asking for help,
"I'd like to go to Dandenong".
To which the answer should be,
"The Dandenong train leaves from platform 5"
and not,
"Well why don't you, then".
Cheers and thank you for having me here, Joy