1) Combined intravenous injection of cocaine
and heroin, more commonly referred to as a speedball
This term is a reference to the American actor and comedian John Belushi (Saturday Night Live, National Lampoons Animal House, etc.) who's death is attributed to an overdose of this drug combination in March of 1982.
2) Synonymous with the phrase bullshit
. The term originates from the accidental mispronunciation of "bullshit" resulting from alcohol intoxication.
This is, again, a reference to John Belushi due to the humorous context of the phrase and its alcohol related origins.
1) Some friends asked if I wanted to try a belushi, but it's a bit too hardcore for my tastes.
2) Man, that is total belushi!