When there is a painfully long cash register line at a local grocery/convenience store, it is common practice for another cashier to open another register. Blinded by the thrill and excitement of an open register, the line-goers have what one would call a store-gasm and rush to the other line, leaving less to zero people in the previous line. A Line Slooth is one who cleverly waits back and watches condescendingly at the fools who rush to the new line.
Annie: Hey, how'd you check out so fast? There was a huge line.
Bob: They opened up a new register. Naturally there was a rush to the new register so I waited back and was the only one left in the first line.
Annie: Classic Line Slooth!