“Can I get…” is not perceived as rude in North America; merely uneducated. Language does drift, but it is worthwhile to fight against drift when it tends to denigrate meaning. As others have pointed out, “Can I get….” is, properly understood, an inquiry about the questioner’s physical ability to go obtain the thing himself. Unless the thing itself doesn’t exist, the proper response to a “Can I get…” question is, “You would know better than I whether you can or not.”