We guess the incident at Black Mesa opened up more portals than the crowbar-wielding scientist could have known. One of which clearly led to Animal Crossing: Wild World, as evidenced by the image to the right. Along with Gordan, you can see a Combine soldier standing about. Why that Combine soldier is probably waiting to knock over a can and force Gordon to dispose of it in the nearest receptacle!
Other cool dress-up scenes include Call of Duty 4, Brokeback Mountain and the Mario brothers' kitchen. Oh, and Hitler. You can't have customization in a video game without creating the world's most evil dude.