Aquinas' arguments

I think that the worst of Aquinas' Five Ways is the fourth one. The Fourth Way says that we are able to judge the good qualities of the things around us because there is a model of every good, which is God. It says that we can see something is ugly because we compare it to our inner knowledge of the perfection of God.
I think this argument is very confusing because what we think of beauty is very different.
for instance, I believe Natalie Portman is VERY beautiful, but there are many people who will disagree with me (namely Emily). Another confusing point in this argument is that Aquinas says that we can know what is ugly, and pretty, based on our knowledge of God. This is confusing because how do we all know this if we've never seen God, or met with him?
it's not like i can recall my brunch with God last week, and remember what He looked like, and be like, oh yeah, Natalie Portman shares traits with him, shes gotta be beautiful.
That's why i don't get his fourth argument, because it makes no sense, to me anyways..