Is it ok to ignore a hot girl at work, since they tend to be scum?

i'm a supervisor, and there are some new hires i have to look after. they are two girls - one is a. bout a 5 in looks, and the other is a 9. to be honest, i favour the 5, since 9s as people tend to scummy overall. I mark her work down harsher, cos i can and since hotties are scum.
why is this bad? i doubt anybody can give me a good reason.
Is it ok to ignore a hot girl at work, since they tend to be scum?
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