Mean can mean you are being rude or in math terms it is adding a set of numbers then dividing by the total amount. ex. If your numbers are 1,2,and 3 add them to get 6 and divide by 3. You get 2.
To get the arithmetic mean you add all the numbers up. Then, count the number of numbers you added, and divide the sum by the toal number of numbers. So the arithmetic mean in math is the average of...
Rude, not polite and kind of nasty. It is can also refer to someone who is not generous or is tight with their money. Try looking the word up in a dictionary.