Idle fish... in this case"Xianyu", the Chinese version of craigslist. I've been living here for the past 6 years.
I always thought it meant salted-fish, until someone corrected me. Something along the lines of spare-fish, unoccupied-fish, idle-fish...
Don't worry, no mother-cursing. I used to live in Newfoundland, there salt-fish is akin to lifeblood, it's a compliment.
It's the pseudonym of the poster of the picture.