Tbf, it took me several (rapid) iterations of the idea before my brain settled on a statement of maximum destruction. The reality is that I'd probably laugh and tell her to go fuck herself or just get confused and inform her that I wasn't intending it to be a date and I'm really not attracted to her in that way; I just thought she might be a cool friend to have (if I'm talking to someone then there's a decent chance we're either friends or will be friends in the near future). I imagine both would probably damage her ego as well, but they'd be no where as devastating as my original comment.
In that vein, after I posted my original comment my brain offered me a slightly better one:
[Start with a pause at the beginning because it creates the illusion that her response was unexpected] "...oh, sorry, everyone said I should give you a chance; I just wanted to be nice. I'm really, really sorry. I know you're a very sweet girl and you'll find the right person who can see you for your strengths."
Id just look with disgust and tell her straight up that nobody wants her not because of her look but because apparently she has an absolute trash personality.
What's the ugliest part of your body?
What's the ugliest part of your body?
Some say your nose
Some say your toes
But I think it's your mind, your mind
I think it's your mind, woo, woo
I remember this MTV commercial/bumper thing which had two punks sitting on a curb.
The guy says, "Nobody likes me." The girl says, "I like you Oliver." He looks at her and says, "Nobody good likes me."
This reminds me of that.