In the beginning of the movie, they are taping "Wayne's World" and Garth is there of course. After they are done taping, Wayne goes outside and for some weird reason Garth pulls up by the sidewalk in the Merth Mobile. But wasn't he just with Wayne? Total Mind blowing!
I'm sorry but I am almost positive that this isn't a slip up. When Wayne is talking to the camera, I believe it is the part where he is by the refrigerator, Garth walks off and you don't see him again until he pulls up in the car.