The speaker is having a terrible day. Noise has pushed them to the edge, and they admit it's "a day for murder." What follows is a grim twist on a job application. Instead of asking people to apply for something good, the speaker invites them to "apply to my gun," as if the weapon were an employer or an office.
The last two lines carry the joke. The gun is "called the state," and it "promises a bed." That bed could be a prison bed, a hospital bed, or a grave. The speaker seems to suggest that the state offers shelter and violence in the same package, and that anyone who signs up gets both.
The title, "Bad apple," adds to this. The speaker may be the rotten one, or may be pointing at a system that spoils its people. The mood is bitter, sarcastic, and unsettling. The poem is short and flat in tone, and that coldness makes the anger feel more real than shouting would.