British expression?

I'm reading Shopaholic Ties the Knot by UK author Sophie Kinsella. There's a scene in which the protagonist's parents embarrass her in front of her boyfriend and she thinks to herself, "Honestly, what are my parents like?" I've also seen it in a Harry Potter book, said by Ron after Hermione argues with him and storms away.

I assume it means something like "What is wrong with them/her?" but I'm wondering how and why. Obviously, this expression isn't native to my dialect. Could someone enlighten me?