So, I’d never really sat down and deconstructed this quote from Bilbo Baggins’ eleventy-first name day party. I just did. The parentheses are there to break it up and make it easier to parse:
“I don’t know (half of) you half as well as I should like”
You say this to someone when you’d like to know them better. He’s saying half the assembled crowd he would like to know better. I think this is a compliment.
“I like (less than half of) you half as well as you deserve”
This is a little trickier, but means that Bilbo acknowledges that there are some people there he doesn’t give enough credit. However, the “less than half” implies that it’s a small number of people. So what he’s really saying here is that there are some who deserve more credit than he gives them, but most people he doesn’t like truly aren’t very good people. It’s an insult hidden inside a compliment, wrapped in a confusing construction.