Crawling Butt Lick

A harsh -albeit immature- generic insult. I guess it's incinuating that the person who this insult is directed to is comparable to something that wriggles around someone's buttocks, licking it (or perhaps the asshole itself) for whatever reason.

British in origin.

It could also imply that the person is a sort of sycophant, ass-kisser, brown-noser, apple-polisher, etc.