You can tell by the reaction people have to Penelope asking Colin to kiss her whether they ever experienced being a wallflower/insecure fat girl at a party or not.
Because you say it's pathetic, I say it's relatable, no matter how desperate it may sound. If you've never had your insecurity eat you up from the inside (but also the outside, as Portia literally told Penelope that she was delusional for thinking she was gonna find a husband in her third season out) to the point you genuinely, wholeheartedly believe no one will ever love you unless you physically change, then obviously the scene is off to you.
But Pen literally told Colin she felt stupid for thinking she's gonna find a husband (she just started believing what the ton and her mother said) and that she knows no one would want to kiss her. And for a romance girl like her, do you think the thought of never having a kiss, never experiencing that passion, would be easy to bear? I can so relate to being the most romantic of the bunch but also being the loneliest and aching for physical and emotional romantic love.
She is so vulnerable and so real in that moment but y'all gotta bitch about it because it doesn't make sense to you. It doesn't make sense to me either because she's gorgeous, but that's the thing - no one ever told her she's gorgeous and actually meant it. And even if they did, there must be 10 more people who didn't that keep that insecurity in her, specifically her sisters and her mother.
Nicola said this one was for the wallflowers, and it truly is, so if you find scenes like this cringe, you just don't relate to the character enough to feel it and recall moments when you had the same thoughts as her.