洗脑 has two common uses: the serious meaning (brainwash/indoctrinate) and the casual internet meaning (something so catchy it gets stuck in your head). 洗脑神曲 (brainwashing hit song) describes an annoyingly catchy tune.
culture
In internet culture, 洗脑 is often used lightheartedly for viral songs, ads, or slogans that you can't get out of your head. But it retains its serious meaning in political and media literacy discussions.