“脱” means “to break away from,” and “粉” is short for “粉丝群,” which means “fan base.” Often used by fans of pop idols, this term means “stop being a fan of.” This usually happens when the pop idol one previously likes gets involved in a scandal or other negative things about them have occured.
Nǐ xǐhuan de nàge gēshǒu zuìjìn yào lái wǒmen shì kāi yǎnchànghuì，nǐ búqù pěngchǎng ma？
The singer you like will come to our city to give a concert shortly. Won’t you want to buy a ticket?
Wǒ yǐjīng tuōfěn le。
I am no longer his fan.