덜렁거리다 (or 덜렁대다) has two major meanings. 1. a loosely connected object dangles around or makes such a noise. e.g. 가방 끈이 끊어져 덜렁거렸다. 2. A person is disorganized and behaves erratically lacking composure (syn: 경망스럽다, 가볍다; ant: 침착하다, 차분하다, 야무지다). e.g. 얘는 늘 침착하지 못하고 덜렁거린다. It is an example of a verb describing a sound or motion. There's a group of them ending in -거리다, -대다, or -하다. For example, - 덜컹거리다/대다 = Something hefty rattles (as a car would on a rough surface). - 퍼덕거리다/퍼덕대다/퍼덕이다 = makes a flapping motion/noise, like a bird's wings, fish out of water, a flag in the wind, etc. - 펄럭거리다/펄럭대다/펄럭이다 = similar but in a lighter and free movement, so it suits a flag or cloth in the wind.

I don't think 덜렁덜렁거리다 is a correct verb. The correct verb would be 덜렁거리다 (notice the space removed between 덜렁 and 거리다 by the way). 덜렁거리다 means 'to dangle/to swing/to flap' For instance 바람에는 빨랫줄에 널린 옷들 덜렁거렸다 (the hanging clothes were flapping in the wind) The use of two 덜렁 (덜렁덜렁거리다) is to emphasize the motion of flapping. It is common to see verbs using the same radical two times, especially for verbs that describes a repetitive motion (e.g. 두근두근하다). 파이팅!