Alternative way to curse about someone or something; less crude and sounds way nicer.
Teacher: Now, students, since you've learnt what is a fish, let me tell you that you can also use 'fish' to replace any bad words that may come out from your mouth.
Student: REALLY?!! What the f-!
Teacher: (interrupts) Ah hah! Replace it with 'fish'.
Student: Aight. I mean what the fish. FIIIIISH! I gotta tell this to my bro!