I'm very surprised that you have such a strong negative response to Shadowheart's joking "I know" line,
Just saying "You are beautifull" – "I know" is very dismissive. If it was meant as a joke (which I firmly believe it wasn't) then it was delivered poorly. Here's how it would actually sound as a joke:
"You are beautiful" - "I know. Unfortunately, I can't say the same about you."
"You are beautiful" - "I know. Laezel already told me that today."
"You are beautiful" - "I know. Why do you think goblins target me the most?"
"You are beautiful" - "I know. I'm just surprised you noticed after a whole bottle of wine."
There has to be something after "I know" otherwise it just sounds like "get lost".
I've noticed a lot of talk about the differences between male and female in previous posts as well, as well as just now saying you gender-swap mod Shadowheart and Lae'zel so that killing them doesn't interfere with your male neurons, so I was wondering something. Could it be that instead of the actual character writing, it's instead because in the base game you find it less offensive if a male Astarion has an "I know" line and much more offensive if a female Shadowheart has such a line, perhaps?
That would turn into a full treatise on my views about men–women relations and roles in the modern world versus the fantasy world. It's just too long and too subjective. I'm not unique - far from it - but I usually find my opinions supported only by a few. So I won't bore readers with my personal crap.
Anyway, I've solved the problem that bothered me, thanks to modding possibilities. If I hadn't been able to do this, it would've been the last Larian game I bought - because I'm not exactly high on opinions about either DoS. And no matter how great a game is, the strength of the aftertaste is what matters in the end. And I had a very, very bad aftertaste when I romanced Laezel and Shadowheart.
So, as an afterword: after casting a very dark forbidden magic on Gale, Wyll, and Astarion - it’s perfectly fine for me (can't say the same for them, though >:D