Maybe it works better in certain contexts with certain folks, and about how you say it?
We can imagine a few scenarios where it'd make somebody laugh 🤭
That said, "You're pretty" sounds low effort.
If we were gonna have somebody say that to us (unlikely), we'd at least want something more like: "Oh my days! You look stunnin' in that outfit sweetie! Totally bangin'!"
(Imagine that said in a typical Essex or London accent.)
