Git-er-done is a statement of boisterous completion or encouraging another person to get something done, completed or finished. It can also be used at random times, such as traffic jams, sports events and oh yes - your favorite I'm sure, Nascar. Its origins are thought by some to be sexual, which it does work well in that context, but its not limited to that. In the last two years Git-er-done has debuted in many social and ethnic settings, thus expanding its borders beyond redneckdome to actual cultural diversity.
Redneck 1: Git-er-done!
Redneck 2: YEAH! GIT-ER-DONE!!
The expression that Larry the Cable Guy uses. Means to fuck, get drunk, get ripped, etc. it basically works for anything of that sort.
Ryan: "Yo Tony, finish off that 2/6 and lets bounce."
Drew: "Ya Tony, Git-er-done!!"
Bryce: "Hey Tony, I think that chick over there is checkin you out... Git-er-done!"