The speaker describes reading, or perhaps receiving, a poem that feels dangerous, as if it passed from mouth to mouth like an infection. The title's play on "unsafe sex" hints at that risky, intimate exchange, though the poem never spells it out. The result is physical: it made the speaker sick.
The second stanza turns to an unsettling image of a heart examined by a hangman with a bad hand. It suggests being judged or probed by someone clumsy and threatening, which makes the scrutiny feel both frightening and a little absurd.
Then the tone shifts. The speaker admits their soul has grown fat on the arts, comfortable and well fed. Being vexed, even made ill, was good for them. The mood is darkly wry and self-mocking. The poem seems to say that art which unsettles us may be worth more than art that simply soothes.