“单身狗”(dan shen gou) was translated into single dog in English. But it did not mean single dogs, it meant single person who didn’t have any boy friend or girl friend containing more or less self-dispraise and self-mockery emotion.
At first, it was some kind of self-mockery for single people. With the popularity of the network language, it was later used for jokes about other people in a single state. Although it has negative meaning, it didn’t have aggression, just entertainment.