How about you just use the AVG application (from the Start Menu) to disable AVG's features and services, rather than killing processes.
http://www.avg.com/au-en/faq.num-4498
As magicandre1981 correctly points out, AVG will protect itself from being shut down even by a user with Admin privileges. Why? Because if you could shut it down, then so could malware that has gained Admin privileges. And that wouldn't be a good thing!
Incidentally, Admin privilages don't give you unlimited powers. Windows still prevents an interactive user with Admin privilages from doing things it deems out of bounds. If I can find some documentation on this I'll add the link here.