Bash is a shortened version of the phrase bashed weed. Bashed weed or "bash" refers to herbal cannabis that has been sprayed with substance to make it weigh more.
bash is a type of herbal canabis that users dislike as the sprayed on substance can make the canabis taste and smoke worse. It is hard to tell what the long term negitive effects of smoking "bash" are as there have been no scientific tests however users of "bash" have complained it can cause irritation to the lungs and throat.
"you want to get some weed off Ted tonite", "fuck that shit its bare bash"
"you want a toke on my spliff", "ok as long as dat shit aint bash"