No one actually knows what it means. It is a quirky little phrase that most people don't really get to use. Its fun to say.
**WARNING: Do not actualy suck on lawn gnomes, they are a choking hazard**

The art of stealing lawn gnomes

A game played with a group of people, after dark. All of the people in the group go to a random house and ring the doorbell of the house. After ringing the door bell everyone poses and holds still on the lawn infront of the house, as if they were lawn gnomes. The first person to move / run loses.

The act of stealing lawn gnomes from people's gardens

Crazy midgit with a pointy hat that stalks you in your sleep.

Little, dwarf-like creatures with pointy red hats. By day, you may see them frolick merrily in people's gardens alongside tulips and fresh soil, though at night they are rumored to steal your undergarments, preferably socks. Some believe this is in protest of them being decorative lawn ornamnents.

Excessive lawn ornamentation.