'Kangaroo on crack' is a metaphor popularized by a very serious publication about depression which only people that have a high IQ can understand.
No one knows what the fuck it actually means, however some have theorized that it refers to the episodes of elated mania people with bipolar disorder suffer. Others have suggested it is a comment on animal testing.
A source recently disclosed the meaning of the phrase. It is, in fact, a reference to certain players in The Last Great Who War. The kangaroo represents Australia (where most of the trolls reside). This, coupled with 'crack', is a comment on how corrupt these people have become. Apparently.