IMO the best thing about Waluigi is that he's simulataniously a blank slate and a very specific character. You've got the basic ground rules of "cheats at sports, plans elaborate schemes, makes loud noises, and holds grudges - including towards himself" but then you can headcanon everything else. Some people might want to view Waluigi as the embodiment of pure hatred, others may see him as a geniunely nice guy who's a little muddled, and some will view him as a mildly anti-social annoyance nobody likes, and that's the beauty of Waluigi's character. He's a blank slate with limitations.
"The enemy of art is the absence of limitation" - Orson Welles (frozen peas guy)
"The enemy of art is the absence of limitation" - Orson Welles (frozen peas guy)