Actually, I think Darcy means this as a compliment to both Elizabeth *and* himself. IMO, he is saying "Neither of us show off or make a big effort in front of people we don't know well enough to know if we respect them or not, no matter how "important" they may be." (That's rather convoluted, but I hope you get my meaning! ;-) I think he is trying to create a bond between them with this remark, sort of like saying "You and I both have good judgement."