The speaker describes a mind that feels frozen and shut off. "Ear of ice" is a striking image: the speaker can't quite take in the world, or maybe has stopped wanting to listen. Against that coldness, the poem sets a swarm of restless activity. Desire is "all the din," and it's compared to ants crawling over a cake, which makes human wanting seem small, busy, and a little grubby. The cake is meant to be sweet, but the ants make it unappealing.
Then comes a glimpse of "people at their sports," seen from the outside, as if the speaker watches other people's games without being able to join in. The last line, "the tin ill morning," is odd and compressed. Judging by the sounds and the word "tin," it suggests a morning that feels cheap, metallic, and sickly.
The mood is detached and weary, with a dry, sour humor. The title "Humbugger" fits that grumpy, dismissive tone, as though the speaker is shrugging at everything.