The speaker admits something most people would hide: shame gives them a thrill. The opening line is blunt and a little boastful, as if confessing were part of the fun. "Prodigious" makes the pleasure sound huge, almost comic, while the word "shame" pulls against it.
The second line is more physical. "My own hands foul my fingers" suggests the speaker is doing something to themselves, and the poem leaves it vague enough that we can read it as guilt over a private act, or as a wider habit of self-blame. Either way, the speaker is both the cause and the one affected.
The last two lines turn into a plea. "Let me suffer for it a little" sounds half-ironic, since the suffering is clearly wanted. The "afternoon bed" feels quiet, idle and secluded. The mood is defiant, intimate and a bit teasing, as the speaker claims the right to feel bad on their own terms.