The phrase janky ass glass refers to low end bongs made of glass from China or other low quality glass. Often this phrase is used to describe goodstash bongs which use a grommet instead a glass on glass joint.
Matt: Dude have you been to skatesurfsmoke in Hermosa? They have goodstash bongs.
Ryan: Yeah I heard about it from some punks who thought they could skate. That place sure does have some janky ass glass.
Matt: I know!! That's exactly what I thought when I walked in there!