NOTE: By coincidence, this phrase is semantically similar to the hip hop colloquialism gully, although the etymology is undoubtedly different.
While gully gully can be similar in meaning to some uses of gully and ghetto, it's chief meaning is wack.
2. A synonym for a crap training shoe.
2. "When I was a kid my mom always made me wear gully gullies to play football in. They were called 'Run Team Pro Shaft 900' and they fell to bits after 2 days!"