From AMLopedia
"Dude, what are you doing?" Was a question often asked by Adam after Liam walked into the upstairs of his house. This all started one day when Liam walked up to where Adam kept his computer and TV. Adam startled him by acting like he didn't know him, and said "Dude, what are you doing?" This freaked Liam out because he forgets stuff every two minutes so he thought he wasn't supposed to come up there.
It got to the point where Adam would say it every time Liam came into his house.