During dinner Mr. Bennet scarcely spoke at all; but when the servants were withdrawn, he thought it time to have some conversation with his guest, and therefore started a subject in which he expected him to shine, by observing that he seemed very fortunate in his patroness. Lady Catherine de Bourgh's attention to his wishes, and consideration for his comfort, appeared very remarkable. Mr. Bennet could not have chosen better. Mr. Collins was eloquent in her praise. The subject elevated him to more than usual solemnity of manner

In this instance, I think that Mr. Bennet is being politely rude. Polite in involving a guest in conversation and rude because he only doing it to be amused by Mr. Collins.