"I AM A BACKDOOR MAN!" (from the episode "Head Case")
To elaborate, unbeknownst to Ramsey (but knownst to us), Parker secretly set up a hidden camera in Ramsey's shower, and broadcast him singing the song "I am a backdoor man" to the entire NNL complex. It remains my favorite moment of the entire series, particularly when Ramsey realizes it, and snarls, "PARKER! I'M GONE KILL YOU!" into the camera).
The first wedding scene from the episode "Two weddings and a funeral". Parker and Olga basically dare each other to marry each other, and each one is expecting the other to back down but neither do.