Someone close to the speaker is celebrating what seems to be a birthday, with cake, friends and a surprise, but the speaker can't join in. The refrain "it's just a Tuesday" sits at the end of almost every stanza, like a flat, tired shrug against all the excitement. The speaker feels stressed and emotionally numb, and the poem hints at something heavier underneath, with lines like "I'm losing my mind" and "cowering in fear."
What makes it sting is the gap between the two people. The celebrator glows "too bright" and doesn't notice anything is wrong. Even the surprise feels hollow, since the speaker had asked for it a week earlier. When they're told not to "ruin this," their silence starts to look like something they're being pushed into. The mood is quiet, tense and lonely. By the final stanza the day simply crawls to a close, and the speaker is still unseen.