CoalJust came back from mining coal
On Chinese internet, "mining coal" and "handling bricks" usually refer to a nickel and dime job, payment is low yet working is hard, and will always mess up your clothing. One can also claim to be working in these two professions, which is basically saying "I'm poor".
It is worth noting that this is actually a kind of stereotype from the past, since modern mine workers and brick handlers in China actually get paid quite well (sometimes having better wages than most white collars). Back in the 80s and 90s? Not so much.