The core of this question is, how much ear abuse can you take? While Despacito is a great song to hear once, I’m pretty sure that if the DJ played it 9 times, I’d fight him too. I’d want to start a mosh pit so we can get everyone to fight and then push the DJ into the moshing lol.
Help the DJ
I’m not even sure why you’d pick this. Who are you? Are you trying hear Despacito for a 10th time? Are you insane? Do you mean help professionally? Perhaps offer the DJ some professional tips as another DJ, like hey man, play a different song. Or perhaps professionally like as a psychiatrist, sit the guy down and be like “okay man, what’s up, why are you obsessed?”
Join him
Fair enough, you see someone go fight the DJ, and the thought comes to you, yeah I’ll help him out, let me fight the DJ too, get this man to stop playing the same song over and over again. You know what they say, it takes at least one follower to get the movement going.
Mosh
Ah, the chaotic neutral option. MOSH MOSH MOSH MOSH! This is the option I would choose. Not only can you start a fight in the crowd, but you can start the mosh and then go for the DJ after anyway. There’s already chaos above, let there be chaos below as well
A Bormal Company 