An exclamation used by hunters, fishers and other country folk when just about anything happens. It's used under any circumstances usually with the phrase "live action" added in before. Hunters will occasionally raise their guns in the air to exclaim a yee yee.
(Yee may be repeated more than twice if appropriate.)
Hunter: let's head out, yee yee!!
Fisher: I got a fish on the line yee yee!
Country bumpkin: mama made apple pie yee yee!
Turtleman: live action yee yee!