See, the difference here is Chuck Norris jokes were simply about exaggerating the strength of a guy with known physical strength. Shaggy jokes can be considered an ironic twist on them in the sense that they juxtapose exaggerated claims of physical strength with the image of a character who, in the canon of his own series, is actually a cowardly twig of a man.

Plus Shaggy jokes are rooted more in fighting anime, specifically Dragon Ball Z; heck, IIRC Frieza outright said something along the lines of "not bad Vegeta, you made me use 10% of my power" at some point.

Its so much better when Fred is unmasking Shaggy, with Shaggy standing right next to him. That's some advanced "I was never really on your side" fuckery.