From the album The Afterparty
This is about revenge that requires the one getting revenge to first destroy herself. She promises to make him suffer when he comes crawling back, but the condition for that power is 'when you're sick of her, I'll be sick of love.' By the time he wants her again, she'll be too emotionally gutted to care. The threat collapses on itself.
Oh my god, I can't even / See her with her long hair, television pretty
She breaks off mid-sentence because finishing the thought would mean admitting she's been watching this woman. 'Television pretty' is specific enough that she's studied her, built a whole mythology around someone whose actual personality she doesn't know.
All my tears are on this dance floor / Mirror, mirror, tell me, am I not as pretty?
She's literally at a party asking where the party went. The Snow White mirror reference turns this into a fairy tale she already knows the ending to. Beauty was supposed to be the thing that kept him, and if she's lost on looks alone, there's no other currency left.
You're gonna beg for it, I'll make you beg for it / When you're sick of her, I'll be sick of love
The power move she's threatening only works if she waits long enough to stop caring entirely. It's not 'when you come back I'll have moved on.' It's 'when you come back I'll have used up my entire capacity to love.' She's announcing her own emotional bankruptcy as if it's a win.
Turn the lights off, light a cigarette / Play a slow song for the old clown
The 'old clown' might be her, not him. She's the one performing heartbreak at the saddest disco, crying on a dance floor, asking mirrors for validation. The slow song is for whoever's still there at closing time, and that person is her.
The saddest part isn't that he left. It's that her entire plan for getting even requires waiting until she's too broken to want him back anyway. She's not threatening to move on. She's threatening to stay exactly where she is until love itself becomes unbearable.