The Stupid Question

Why do people ask the question, "May I ask you a question?" Has anyone ever realized that they are asking a question about weather or not they can ask a question? I mean the question mark is clearly there , just look (don't worry it only requires a slight movement of the eyes, won't even burn a calaorie). And how do you answer that question, Yes but only one, (which they already asked?!). Or what if you say no, "to late I already did, haha sucker!" Any way its kinda fun to think about the implications.