Rick and Angela are two characters who have their own concept of beauty, but it is diametrically opposed. Angela considers herself beautiful and poses in the window, while Rick is much more attracted to the mystery in Jane. Rick tells Angela in direct text that she is boring and ordinary, which makes the girl very upset. And at the end of Angela's arc, we see that all her self-confidence and seductiveness is actually contrived, because when it comes to actually having sex with Lester, she turns out to be a virgin. She even wears a white shirt in this scene to emphasise her innocence.
And Lester, who has spent the whole film imagining the moment of intimacy with Angela and idealising their sex, does not take advantage of the girl's defencelessness. Although for him she has not become worse or more boring - she is still the same beautiful red rose, because Lester is not Rick, he is much less sophisticated in matters of visuals and beauty, and has only just begun his journey into her knowledge. It's a pity that the journey was so short, because Lester is a beautiful person - look at his smile in the last scene and listen to his last monologue. He has transformed from a grumpy, disgruntled grump into a bright man who loves life so much.