So I've been wondering, what kind of flaws in a mesh will make the sims crash? (or make annoying glitches for the game) Is it just luck if you manage to make a mesh that wont make game crash, but works perfectly? I guess there are the obvious ones like if the mesh is too big for your computer to handle, or if you screw up the boneassigments badly, or dont have them at all. But what other reasons are there?

Usually, when I've crashed the game with a mesh, it's due to bad or missing mesh comments or no bone assignments. There are plenty of things which cause wtf glitches, but those are generally really stupid things like taking a child mesh and enabling it for adults: actual crashes are quite rare.