1. When all else fails, make it an "ism".
2. A negative stereotype stating that because one has little or no interest in their personal hygiene, appearance, or social aptness, they are typically dull, ugly, and unsavory people. Unlike other stereotypes, this one tends to be true.
3. A side effect of natural selection and survival of the fittest.
"You won't hire me because you're lookist!"
"No, I won't hire you because your inability to fit in with society is not fit to represent my company, and because your sloth in your hygiene probably represents a lack of concern for many other things besides your personal appearance. Plus, accusing people of lookism for not wanting to associate with your smelly ass is pretty stupid."