One interpretation of this song is that it's about heroin:
"Come doused in mud, served in bleach, as I want you to be" - Drugs are cut with all kinds of rubbish.
"As a friend, as a trend, as a known enemy" - Drugs can make you feel good, like a friend. There's a trend with them, but they are bad (thus, "as a known enemy.")
"Well I swear that I don't have a gun" - A gun could mean a syringe. Cobain also mentions a gun in 'Smells Like Teen Spirit
"Load up on guns, bring your friends its fun to lose and to pretend" - Losing could mean giving in to drugs, and feeling high is to pretend. (thanks, James - Melbourne, Australia)